Bra Size Calculator

What to calculate

What would you like to do? Quick mode needs two measurements. Advanced mode adds four more — loose and tight under-bust, leaning and lying bust — and uses the spread between them to grade how stable the estimate is instead of guessing.

Units Every measurement below is read in this unit and converted to millimetres with the exact definition 1 in = 2.54 cm. Nothing is rounded before the sizing rules run.

Sizing system Each system has its own band ladder and its own cup ladder, and each is applied to your measurements by its own published rule. Switching does not convert a size — it re-derives one.

Your two reference measurements

Snug under-bust Directly under the bust, in the crease where the breast tissue ends. Tape firm and level all the way round, taken at the end of a relaxed breath out. This reading is used raw — nothing is added to it.

Standing bust Across the fullest part of the bust, standing upright, tape horizontal and not compressing. Same relaxed breath out.

Take both at the end of a relaxed breath out. Breathing in raises the calculated band and lowers the calculated cup, so the breathing state is part of the measurement.

Measure twice (optional)

Measure twice and average Turning this on adds a second field for each of the two reference measurements. Where both are filled in, the tool uses their arithmetic mean and shows the averaging step in the calculation receipt.

Snug under-bust — second reading Optional. Used only when the measure-twice option above is on.

Standing bust — second reading Optional. Used only when the measure-twice option above is on.

Where both readings are filled in the tool uses their arithmetic mean, and the averaging step appears in the calculation receipt so it is never hidden.

Advanced measurement

Loose under-bust Advanced mode only. Same position, tape resting against the body with no tension at all.

Tight under-bust Advanced mode only. Same position, tape pulled firmly — as tight as a band you would still find comfortable.

Leaning bust Advanced mode only. Bend forward from the hips to about 90 degrees, let the tissue hang, and measure across the fullest part.

Lying bust Advanced mode only. Lie flat on your back and measure across the fullest part of the bust.

These four are optional and are never used to override the two reference readings. They are used to see how far your own measurements move the answer, which is what the measurement-stability grade reports.

Your starting bra size

34DD UK

Measurement estimate

Likely range: 34DD (every method and every reading you gave lands here)

This calculator estimates a starting bra size. It does not determine a universally correct size.

Band

34

Designates an under-bust girth of 83.8-88.9 cm

Cup

DD

Step 5 on the UK ladder: a difference of 12.7-15.2 cm

Measurement stability

High

How much your own readings move the answer

Source agreement

Strong

How far apart the documented methods land

Sister sizes

32E · 36D

Approximately the same nominal cup volume on a different band

Your bra size, and what to try first

Try these first, in this order

34DD UKThe size your reference readings designate under the primary documented method. Start here.
32E UKBand feels too loose in the size above: A shorter band with one more cup step keeps the nominal cup volume roughly comparable while giving the band something to grip.
36D UKBand feels too tight in the size above: A longer band with one fewer cup step keeps the nominal cup volume roughly comparable while easing the ribcage.

The same measurements in every supported system

The same two measurements under each system’s own rule, and what a printed conversion chart would say
System	Your measurements under that system’s own rule	Printed label conversion from 34DD	Agreement
UK (selected)	34DD	—	—
US / Canada	34DD	34DD	Strong
EU	85B	75E	Variable
France / Spain	100B	90E	Variable
Australia / NZ	12DD	12DD	Strong
Japan	85C	75E	Variable

Where the two columns disagree, neither is declared correct. The left column is what your body measures under that country’s own published rule. The right column is what a manufacturer’s conversion chart prints, and those charts carry the legacy additive band convention, which sits about four inches — roughly two European steps — above a raw under-bust reading.

Why this result — the calculation receipt

Everything below comes from the engine that produced the size above. Between them these steps are enough to reproduce the result by hand from your own tape readings.

Question: What bra size should I start with in UK sizing?
Raw inputs: mode measure; system uk; unit cm; snug under-bust 86 cm; standing bust 100 cm
Normalized inputs: under-bust 86 cm (33.86 in), bust 100 cm (39.37 in)
Exact conversion: 1 in = 2.54 cm exactly; every reading is held in millimetres and is not rounded before a rule runs
Method: Take the snug under-bust reading as it is and put it on the nearest rung of that system's band ladder — the nearest even inch, or the nearest five centimetres. Nothing is added.
Formula / rules applied: Band = the snug under-bust girth in inches placed on the even-inch ladder. Band B designates an under-bust girth from B minus one to B plus one inches. Cup step = the bust girth in inches minus the band number, one inch to a step. Step 0 is AA, step 4 is D, step 5 is DD, step 6 is E, and the ladder continues with the UK double letters.
Substitution: under-bust 86 cm → band 34; difference 13.6 cm → cup DD
Steps: Snug under-bust: 86 cm = 860 mm (exact, 1 in = 25.4 mm; not rounded before the rules run).
Standing bust: 100 cm = 1000 mm (exact, 1 in = 25.4 mm; not rounded before the rules run).
Band: Band = the snug under-bust girth in inches placed on the even-inch ladder. Band B designates an under-bust girth from B minus one to B plus one inches. → 34 (designates an under-bust girth of 83.8-88.9 cm).
Cup: Cup step = the bust girth in inches minus the band number, one inch to a step. Step 0 is AA, step 4 is D, step 5 is DD, step 6 is E, and the ladder continues with the UK double letters. → difference of 13.6 cm falls in the DD interval (12.7-15.2 cm).
Source votes (documented methods, legacy excluded): Nearest step → 34DD; Round up → 34DD.
Source agreement: Strong (methods at most 0 ladder step(s) apart across 2 methods).
Measurement stability: High (spread 0 ladder step(s)).
Measurement-supported range: 34DD.
Selected system: UK
Result: 34DD UK
Assumptions: Every reading was taken at the end of a relaxed breath out, tape horizontal and level.
This is a starting size in one sizing convention, not a verified physical fit.
Warnings: This calculator estimates a starting bra size. It does not determine a universally correct size.
Independent check (passed): Reverse check: the 34 band designates 83.8-88.9 cm and the DD cup designates a 12.7-15.2 cm difference; your readings fall inside both intervals. No independent authority verifies that this size will fit you; only the arithmetic and the ladder membership are checked here.
Precision and rounding: All classification arithmetic runs on unrounded millimetres. Inputs in centimetres are multiplied by 10 and inputs in inches by exactly 25.4; nothing is rounded before a band or cup interval is decided. Rounding happens only in the view layer, and the receipt records the unrounded values it was given.
Source dataset version: bra-size-systems v1.0.0 · bra-size-source-charts v1.0.0
Engine version: bra-size-engine v1.0.0 · receipt format v1.0.0

Sources behind this result

No single owning authority — a labelling convention published consistently by independent manufacturers and fitting guides across the United Kingdom, Ireland, the United States, Canada, Australia and New Zealand — Even-inch band ladder and one-inch cup step Tier 3 · convention-documented-no-single-authority · reviewed 2026-08-10
Biomechanics Research Laboratory, University of Wollongong — published in British Journal of Sports Medicine (BMJ) — McGhee DE, Steele JR. How do respiratory state and measurement method affect bra size calculations? Br J Sports Med. 2006;40(12):970-974. Tier 1 · doi-record-verified · reviewed 2026-08-10
Department of Sport and Exercise Science, University of Portsmouth — published in Ergonomics (Taylor & Francis) — White J, Scurr J. Evaluation of professional bra fitting criteria for bra selection and fitting in the UK. Ergonomics. 2012;55(6):704-711. Tier 1 · doi-record-verified · reviewed 2026-08-10
Biomechanics Research Laboratory, University of Wollongong — published in British Journal of Sports Medicine (BMJ) — McGhee DE, Steele JR. How do respiratory state and measurement method affect bra size calculations? Br J Sports Med. 2006;40(12):970-974. Tier 1 · doi-record-verified · reviewed 2026-08-10
Department of Sport and Exercise Science, University of Portsmouth — published in Ergonomics (Taylor & Francis) — White J, Scurr J. Evaluation of professional bra fitting criteria for bra selection and fitting in the UK. Ergonomics. 2012;55(6):704-711. Tier 1 · doi-record-verified · reviewed 2026-08-10
No single owning authority — a labelling convention published consistently by independent manufacturers and fitting guides across the United Kingdom, Ireland, the United States, Canada, Australia and New Zealand — Even-inch band ladder and one-inch cup step Tier 3 · convention-documented-no-single-authority · reviewed 2026-08-10
No single owning authority — the centimetre band and cup convention used across continental European labelling, consistent with the interval principle of EN 13402-3:2017 — Five-centimetre European band ladder and two-centimetre cup progression Tier 3 · convention-documented-no-single-authority · reviewed 2026-08-10

How accurate is this, specifically

Two different uncertainties are reported separately, because they have different cures. Neither is expressed as a percentage: neither is a sample from any distribution, so a percentage would be decoration rather than measurement.

Measurement stability: High

Every one of your readings, and every combination of them, lands on the same size, and no reading sits within the boundary margin of the next interval.

Only one pair of readings was supplied, so there is no spread to measure. Adding a second reading, or switching to the six-measurement mode, is what would test this.

Source agreement: Strong

Every non-legacy method registered for this system lands on the same band and the same cup.

Snug under-bust, nearest step on the ladder → 34DD
Snug under-bust, rounded up to the next step → 34DD

Boundary proximity

Neither of your readings sits within a quarter of an inch of an interval edge, so a small change in tape tension would not move this result.

What could still be wrong

This calculator estimates a starting bra size. It does not determine a universally correct size.

6.35 mm is exactly one quarter of an inch. A reading that falls within this distance of the edge of its band or cup interval is reported as sitting near a boundary, because a quarter of an inch is well inside the difference a change of tape tension or breathing state can produce. It is a disclosed CalcDomain modelling choice, not a measured tolerance, and it never changes which interval a reading falls in.

Check the bra you are already wearing

A size and a fit are different questions. McGhee and Steele (2010) assessed 104 women and found 85% were wearing a bra that did not fit by professional criteria, and that sizes from standard measurement systems differed significantly from the size professional fit criteria produced. Tick what you can actually see and feel; the diagnosis is deterministic and the rule it matched is named.

The bra you are wearing

Sizing system on the label The system whose ladder the printed size belongs to.

Band The number printed on the label.

Cup The letter printed on the label.

Wired or wireless The underwire questions are only asked, and only read, when the bra is wired.

Band

The band does most of the work of holding a bra up. It is checked first because a band that is not doing its job changes what everything else looks like.

The band stays level all the way round, parallel with the floor. The band rides up at the back. The band is painfully tight or restricts breathing. The band shifts or lifts when you raise your arms. There is strong tissue bulging above or below the band.

Cups

The cups are where incorrect fit is most often observed. Containment, spilling, wrinkling and cutting are separate observations and are read separately.

All the breast tissue sits inside the cup. Tissue spills over the top edge of the cup. Tissue spills out at the sides, under the arm. The cup wrinkles, gapes or has empty space in it. The edge of the cup cuts into the tissue and leaves a line. The cups look and feel about right.

Underwire

Only asked when the bra is wired. Wire problems are frequently geometry problems rather than size problems.

The wire sits all the way around the breast tissue, on the ribcage. The wire sits on breast tissue rather than behind it. The wire digs in or is painful. The wire is narrower than the base of the breast. The wire is wider than the base of the breast and sits out under the arm.

Front band and gore

The centre panel between the cups. What it does is informative, but on its own it settles very little.

The centre panel sits flat against the sternum. The centre panel floats away from the chest.

Straps

Straps are the least diagnostic component for size. Nothing here alone changes a size recommendation.

The straps are comfortable and stay where they are. The straps slide off the shoulders. The straps dig into the shoulders. The straps cannot be adjusted short or long enough.

Fit check for 34DD UK (wired)

Likely a band-size issue

The evidence points at the band rather than the cups. Because band and cup are defined relative to each other, moving the band one step means moving the cup one step the other way to keep roughly the same cup volume.

The band is not anchored, and the cups are not reporting a problem. One band size down with one cup size up keeps the nominal cup volume roughly where it is while giving the band something to grip.

Size to try next: 32E

What you reported, and what it means

The band rides up at the back.

Likely causes

The band is longer than the body it is on, so the weight at the front pulls the back upwards.
The band has stretched with wear and is being worn on the loosest hook.

What to try

Try the same bra on a tighter hook first — that is free and it is the fastest test.
If it is already on the tightest hook, try one band size down, and go one cup size up at the same time so the cup volume is roughly preserved.

This observation is strong enough on its own to move a size.

Caveats

Sufficient on its own only when the cups are not also reporting a problem; a riding band with spilling cups is read as a mixed sizing issue rather than a band issue.

The cups look and feel about right.

Likely causes

No cup problem is being reported.

What to try

Nothing to change here.

This observation is NOT enough on its own to change a size.

Signal weights the rule was matched on

Deterministic signal weights from the versioned fit-criteria dataset
Signal	Weight	Observations
band-loose	2	1
band-tight	0	0
cup-small	0	0
cup-large	0	0
shape	0	0

Rule matched: band-too-loose. Rules are evaluated in the fixed order recorded in the dataset and the first match wins, so the same answers always give the same diagnosis.

Visual bra fit guide

Eight schematic diagrams drawn here as inline SVG — no photographs, no stock imagery and no image request. Each one pairs what you see with what usually causes it and what to try, and each carries the same information in text.

Correct fit

What you see Band level all the way round, cups smooth and full, centre panel flat, straps sitting still.

Likely cause Band length, cup volume and wire width all suit this body.

What to try Nothing. Note the size and the style — the style is half the reason it works.

Band riding up at the back

What you see The band sits higher at the back than at the front.

Likely cause The band is longer than the ribcage it is on, so the weight at the front pulls the back upward.

What to try A tighter hook first. If it is already on the tightest hook, one band size down with one cup size up.

Cup spilling over

What you see Tissue bulging over the top edge or out at the side of the cup.

Likely cause Not enough cup volume, or a cup cut too shallow for how the tissue sits.

What to try Same band, one cup size up. If a fuller-cut style fixes it at the current size, the cut was the problem.

Cup gaping or wrinkling

What you see Loose fabric, wrinkles or visible empty space in the cup.

Likely cause More volume than is being filled — OR a cup cut deeper than the tissue projects — OR a loose band holding the cup away.

What to try Check the band first. Then a shallower or moulded cut at the same size. One cup down only as a test.

Wire sitting on tissue

What you see The underwire rests on the breast itself instead of behind it on the ribcage.

Likely cause The cup is too small to let the wire reach the ribcage — or the wire is too narrow for the breast root.

What to try One cup up in the same band. If the wire still does not drop, look for a wider wire, not more volume.

Floating centre gore

What you see The panel between the cups stands away from the breastbone.

Likely cause Not enough cup volume, a cup too shallow, a wire too narrow, or a chest that is simply not flat there.

What to try One cup up as a test. Then a lower or narrower centre panel. If neither helps, it is geometry, not size.

Straps digging in

What you see Grooves or soreness where the straps sit on the shoulders.

Likely cause The band is not carrying enough of the load, so the straps are — or the straps are narrow for the load.

What to try Loosen the straps and tighten the band. If the digging stops, it was the band. Never change size on this alone.

Straps sliding off

What you see The straps slip off the shoulders through the day.

Likely cause Straps set too wide for these shoulders, not adjusted short enough, or shoulders that slope more than the style assumes.

What to try Shorten the straps, then look for a style with straps set closer in or a racer-back option. This carries no size information.

Sister sizes

A sister size keeps the nominal cup volume approximately the same on a different band: one band down with one cup up, or one band up with one cup down. The steps below are read from the ladder of the system you selected, so nothing here assumes that D is followed by DD or that DD is followed by E — in the European ladder it is not.

Sister sizes for 34DD on the UK ladder
If the band feels…	Try	Why
Band feels too loose	32E	A shorter band with one more cup step keeps the nominal cup volume roughly comparable while giving the band something to grip.
Band feels too tight	36D	A longer band with one fewer cup step keeps the nominal cup volume roughly comparable while easing the ribcage.

Sister sizing keeps the nominal cup volume approximately comparable within one system's convention. It does not guarantee the same fit, the same wire width, the same cup depth or the same construction.

Convert a bra size, and browse the chart

Converting a label and converting a body are two different operations, and they do not always agree. This converter does both and tells you when they diverge, instead of quietly picking one.

34DD UK in EU

75E EU

Observed equivalent range: 75E

Closest supported equivalent Agreement: Variable

The two ways of answering this disagree

Printed conversion chart: 75E EU

EU sizing’s own measurement rule: 85A EU

These two answers are 4 ladder steps apart, and the gap is not a rounding artefact. A printed conversion chart maps the LABEL: it assumes the inch size was assigned the traditional way, with roughly four inches added to the under-bust reading. The second answer maps the BODY: it takes the under-bust and bust girths that 34DD UK designates and applies EU sizing’s own published measurement rule to them. If your current size came from a shop’s tape measure, the label answer is the one to buy in. If you arrived at it by measuring your own under-bust and using it raw, the body answer is closer to what your measurements say.

All supported systems

34DD UK across every system this calculator supports
System	Size	Also printed as	Sources agree
UK (source)	34DD	—	strong
US / Canada	34DD	E	moderate
EU	75E	—	strong
France / Spain	90E	—	strong
Australia / NZ	12DD	E	variable
Japan	75E	—	moderate

Two bras of the same nominal size from different brands can fit differently. A converted label is a starting point in the target system, not a guarantee.

Sister sizes for 34DD

Sister sizes on the UK ladder
If the band feels…	Try	Why
Band feels too loose	32E	A shorter band with one more cup step keeps the nominal cup volume roughly comparable while giving the band something to grip.
Band feels too tight	36D	A longer band with one fewer cup step keeps the nominal cup volume roughly comparable while easing the ribcage.

Sister sizing keeps the nominal cup volume approximately comparable within one system's convention. It does not guarantee the same fit, the same wire width, the same cup depth or the same construction.

Browse the cross-system chart

Every cup on the 34 UK band, across all supported systems. Generated by the same conversion the converter above uses.
Cup step	UK	US	EU	FR	AU	JP
0	34AA	34AA	75AA	90AA	12AA	75AA
1	34A	34A	75A	90A	12A	75A
2	34B	34B	75B	90B	12B	75B
3	34C	34C	75C	90C	12C	75C
4	34D	34D	75D	90D	12D	75D
5	34DD	34DD	75E	90E	12DD	75E
6	34E	34DDD	75F	90F	12E	75F
7	34F	34DDDD	75G	90G	12F	75G
8	34FF	34H	75H	90H	12FF	75H
9	34G	34I	75I	90I	12G	75I
10	34GG	34J	75J	90J	12GG	75J
11	34H	34K	75K	90K	12H	—
12	34HH	—	75L	90L	12HH	—
13	34J	—	—	—	12J	—
14	34JJ	—	—	—	12JJ	—
15	34K	—	—	—	12K	—
16	34KK	—	—	—	—	—
17	34L	—	—	—	—	—

Systems this calculator does not support

China — No band or cup ladder could be given a defensible rule from a source available here. Zheng, Yu and Fan (2007) developed a new Chinese bra sizing system specifically because the existing mapping did not serve that population well, which is itself evidence that no single Chinese ladder can be asserted. Nothing is estimated.
Italy — Italian bra bands are printed as small ordinal numbers rather than as a measurement, and the anchor between that ordinal ladder and an under-bust girth could not be established from a source available here. Guessing an anchor would put every Italian answer one or two bands out, so no Italian conversion is offered.
South Korea — Korean bra sizing uses a centimetre band ladder whose step and anchor could not be verified from a source available here. It is left unsupported rather than approximated from the Japanese ladder, which would be an assumption, not a conversion.
Brazil — Brazilian bra sizing uses its own numeric band ladder with no verifiable published anchor to an under-bust girth reachable from here. Not estimated.
India — Indian retail bra sizing largely reuses inch band numbers but with no single published cup convention that could be verified here. Rather than silently treat it as the United States ladder, it is declared unsupported.

Bra size chart — every band and what it designates

These tables are generated by the same catalog the calculator computes from. There is no second table of numbers anywhere on this page: change the dataset and the calculator and the chart move together.

UK band ladder — every band and the under-bust girth it designates. Band = the snug under-bust girth in inches placed on the even-inch ladder. Band B designates an under-bust girth from B minus one to B plus one inches.
Band	Under-bust (cm)	Under-bust (in)
26	63.5–68.6	25.0–27.0
28	68.6–73.7	27.0–29.0
30	73.7–78.7	29.0–31.0
32	78.7–83.8	31.0–33.0
34	83.8–88.9	33.0–35.0
36	88.9–94.0	35.0–37.0
38	94.0–99.1	37.0–39.0
40	99.1–104.1	39.0–41.0
42	104.1–109.2	41.0–43.0
44	109.2–114.3	43.0–45.0
46	114.3–119.4	45.0–47.0
48	119.4–124.5	47.0–49.0
50	124.5–129.5	49.0–51.0

US / Canada band ladder — every band and the under-bust girth it designates. Band = the snug under-bust girth in inches placed on the even-inch ladder, identical to the UK band rule. Band B designates an under-bust girth from B minus one to B plus one inches.
Band	Under-bust (cm)	Under-bust (in)
26	63.5–68.6	25.0–27.0
28	68.6–73.7	27.0–29.0
30	73.7–78.7	29.0–31.0
32	78.7–83.8	31.0–33.0
34	83.8–88.9	33.0–35.0
36	88.9–94.0	35.0–37.0
38	94.0–99.1	37.0–39.0
40	99.1–104.1	39.0–41.0
42	104.1–109.2	41.0–43.0
44	109.2–114.3	43.0–45.0
46	114.3–119.4	45.0–47.0
48	119.4–124.5	47.0–49.0
50	124.5–129.5	49.0–51.0

EU band ladder — every band and the under-bust girth it designates. Band = the snug under-bust girth in centimetres placed on the five-centimetre ladder. Band N designates an under-bust girth from N minus 2.5 to N plus 2.5 centimetres, which is the interval principle EN 13402-3:2017 sets out for size labelling.
Band	Under-bust (cm)	Under-bust (in)
55	52.5–57.5	20.7–22.6
60	57.5–62.5	22.6–24.6
65	62.5–67.5	24.6–26.6
70	67.5–72.5	26.6–28.5
75	72.5–77.5	28.5–30.5
80	77.5–82.5	30.5–32.5
85	82.5–87.5	32.5–34.4
90	87.5–92.5	34.4–36.4
95	92.5–97.5	36.4–38.4
100	97.5–102.5	38.4–40.4
105	102.5–107.5	40.4–42.3
110	107.5–112.5	42.3–44.3

France / Spain band ladder — every band and the under-bust girth it designates. The same under-bust ladder as the European system, with 15 added to the printed number: where Europe prints 75, France and Spain print 90.
Band	Under-bust (cm)	Under-bust (in)
70	52.5–57.5	20.7–22.6
75	57.5–62.5	22.6–24.6
80	62.5–67.5	24.6–26.6
85	67.5–72.5	26.6–28.5
90	72.5–77.5	28.5–30.5
95	77.5–82.5	30.5–32.5
100	82.5–87.5	32.5–34.4
105	87.5–92.5	34.4–36.4
110	92.5–97.5	36.4–38.4
115	97.5–102.5	38.4–40.4
120	102.5–107.5	40.4–42.3
125	107.5–112.5	42.3–44.3

Australia / NZ band ladder — every band and the under-bust girth it designates. The same even-inch under-bust ladder as the UK, with the printed number reduced by 22: a 34-inch under-bust ladder rung is printed as 12.
Band	Under-bust (cm)	Under-bust (in)
4	63.5–68.6	25.0–27.0
6	68.6–73.7	27.0–29.0
8	73.7–78.7	29.0–31.0
10	78.7–83.8	31.0–33.0
12	83.8–88.9	33.0–35.0
14	88.9–94.0	35.0–37.0
16	94.0–99.1	37.0–39.0
18	99.1–104.1	39.0–41.0
20	104.1–109.2	41.0–43.0
22	109.2–114.3	43.0–45.0
24	114.3–119.4	45.0–47.0
26	119.4–124.5	47.0–49.0
28	124.5–129.5	49.0–51.0

Japan band ladder — every band and the under-bust girth it designates. Band = the snug under-bust girth in centimetres on the five-centimetre ladder, as in Europe.
Band	Under-bust (cm)	Under-bust (in)
60	57.5–62.5	22.6–24.6
65	62.5–67.5	24.6–26.6
70	67.5–72.5	26.6–28.5
75	72.5–77.5	28.5–30.5
80	77.5–82.5	30.5–32.5
85	82.5–87.5	32.5–34.4
90	87.5–92.5	34.4–36.4
95	92.5–97.5	36.4–38.4
100	97.5–102.5	38.4–40.4
105	102.5–107.5	40.4–42.3

Cup size chart — every cup and the difference it designates

Read these with the basis in mind. The inch systems take the cup from the bust minus the band number; the centimetre systems take it from the bust minus the under-bust girth. That is a structural difference, not a rounding difference.

UK cup ladder — basis: bust girth minus the band number. Cup step = the bust girth in inches minus the band number, one inch to a step. Step 0 is AA, step 4 is D, step 5 is DD, step 6 is E, and the ladder continues with the UK double letters.
Step	Cup	Also printed as	Difference (cm)	Difference (in)	Sources agree
0	AA	—	0.0–2.5	0.00–1.00	strong
1	A	—	2.5–5.1	1.00–2.00	strong
2	B	—	5.1–7.6	2.00–3.00	strong
3	C	—	7.6–10.2	3.00–4.00	strong
4	D	—	10.2–12.7	4.00–5.00	strong
5	DD	—	12.7–15.2	5.00–6.00	strong
6	E	—	15.2–17.8	6.00–7.00	strong
7	F	—	17.8–20.3	7.00–8.00	strong
8	FF	—	20.3–22.9	8.00–9.00	strong
9	G	—	22.9–25.4	9.00–10.00	strong
10	GG	—	25.4–27.9	10.00–11.00	moderate
11	H	—	27.9–30.5	11.00–12.00	moderate
12	HH	—	30.5–33.0	12.00–13.00	moderate
13	J	—	33.0–35.6	13.00–14.00	moderate
14	JJ	—	35.6–38.1	14.00–15.00	moderate
15	K	—	38.1–40.6	15.00–16.00	moderate
16	KK	—	40.6–43.2	16.00–17.00	variable
17	L	—	43.2–45.7	17.00–18.00	variable

US / Canada cup ladder — basis: bust girth minus the band number. Cup step = the bust girth in inches minus the band number, one inch to a step. The ladder runs AA, A, B, C, D and then repeats the letter D — DD, DDD, DDDD — where UK inserts E, F and G.
Step	Cup	Also printed as	Difference (cm)	Difference (in)	Sources agree
0	AA	—	0.0–2.5	0.00–1.00	strong
1	A	—	2.5–5.1	1.00–2.00	strong
2	B	—	5.1–7.6	2.00–3.00	strong
3	C	—	7.6–10.2	3.00–4.00	strong
4	D	—	10.2–12.7	4.00–5.00	strong
5	DD	E	12.7–15.2	5.00–6.00	moderate
6	DDD	F	15.2–17.8	6.00–7.00	moderate
7	DDDD	G, 4D	17.8–20.3	7.00–8.00	variable
8	H	5D	20.3–22.9	8.00–9.00	variable
9	I	—	22.9–25.4	9.00–10.00	variable
10	J	—	25.4–27.9	10.00–11.00	variable
11	K	—	27.9–30.5	11.00–12.00	variable

EU cup ladder — basis: bust girth minus under-bust girth. Cup step = the bust girth minus the under-bust girth in centimetres, two centimetres to a step, with AA covering 10 to 12 centimetres and A covering 12 to 14. The ladder is a single run of letters with no double letters.
Step	Cup	Also printed as	Difference (cm)	Difference (in)	Sources agree
0	AA	—	10.0–12.0	3.94–4.72	moderate
1	A	—	12.0–14.0	4.72–5.51	strong
2	B	—	14.0–16.0	5.51–6.30	strong
3	C	—	16.0–18.0	6.30–7.09	strong
4	D	—	18.0–20.0	7.09–7.87	strong
5	E	—	20.0–22.0	7.87–8.66	strong
6	F	—	22.0–24.0	8.66–9.45	strong
7	G	—	24.0–26.0	9.45–10.24	strong
8	H	—	26.0–28.0	10.24–11.02	moderate
9	I	—	28.0–30.0	11.02–11.81	moderate
10	J	—	30.0–32.0	11.81–12.60	moderate
11	K	—	32.0–34.0	12.60–13.39	variable
12	L	—	34.0–36.0	13.39–14.17	variable

France / Spain cup ladder — basis: bust girth minus under-bust girth. Identical to the European cup rule and the European letter ladder.
Step	Cup	Also printed as	Difference (cm)	Difference (in)	Sources agree
0	AA	—	10.0–12.0	3.94–4.72	moderate
1	A	—	12.0–14.0	4.72–5.51	strong
2	B	—	14.0–16.0	5.51–6.30	strong
3	C	—	16.0–18.0	6.30–7.09	strong
4	D	—	18.0–20.0	7.09–7.87	strong
5	E	—	20.0–22.0	7.87–8.66	strong
6	F	—	22.0–24.0	8.66–9.45	strong
7	G	—	24.0–26.0	9.45–10.24	strong
8	H	—	26.0–28.0	10.24–11.02	moderate
9	I	—	28.0–30.0	11.02–11.81	moderate
10	J	—	30.0–32.0	11.81–12.60	moderate
11	K	—	32.0–34.0	12.60–13.39	variable
12	L	—	34.0–36.0	13.39–14.17	variable

Australia / NZ cup ladder — basis: bust girth minus the band number. Cup step = the bust girth in inches minus the inch-ladder band number, one inch to a step, on the UK letter ladder.
Step	Cup	Also printed as	Difference (cm)	Difference (in)	Sources agree
0	AA	—	0.0–2.5	0.00–1.00	strong
1	A	—	2.5–5.1	1.00–2.00	strong
2	B	—	5.1–7.6	2.00–3.00	strong
3	C	—	7.6–10.2	3.00–4.00	strong
4	D	—	10.2–12.7	4.00–5.00	strong
5	DD	E	12.7–15.2	5.00–6.00	variable
6	E	DDD	15.2–17.8	6.00–7.00	variable
7	F	—	17.8–20.3	7.00–8.00	variable
8	FF	G	20.3–22.9	8.00–9.00	variable
9	G	—	22.9–25.4	9.00–10.00	variable
10	GG	—	25.4–27.9	10.00–11.00	variable
11	H	—	27.9–30.5	11.00–12.00	variable
12	HH	—	30.5–33.0	12.00–13.00	variable
13	J	—	33.0–35.6	13.00–14.00	variable
14	JJ	—	35.6–38.1	14.00–15.00	variable
15	K	—	38.1–40.6	15.00–16.00	variable

Japan cup ladder — basis: bust girth minus under-bust girth. Cup step = the bust girth minus the under-bust girth in centimetres, 2.5 centimetres to a step, starting at AAA for 2.5 to 5 centimetres. The Japanese ladder therefore has one more rung at the bottom than the European one, which is why the same letter does not name the same step in the two systems.
Step	Cup	Also printed as	Difference (cm)	Difference (in)	Sources agree
0	AAA	—	2.5–5.0	0.98–1.97	moderate
1	AA	—	5.0–7.5	1.97–2.95	moderate
2	A	—	7.5–10.0	2.95–3.94	moderate
3	B	—	10.0–12.5	3.94–4.92	moderate
4	C	—	12.5–15.0	4.92–5.91	moderate
5	D	—	15.0–17.5	5.91–6.89	moderate
6	E	—	17.5–20.0	6.89–7.87	moderate
7	F	—	20.0–22.5	7.87–8.86	moderate
8	G	—	22.5–25.0	8.86–9.84	variable
9	H	—	25.0–27.5	9.84–10.83	variable
10	I	—	27.5–30.0	10.83–11.81	variable
11	J	—	30.0–32.5	11.81–12.80	variable

Cup sizes in order, and the cup size explorer

Pick any band and cup to see exactly what that rung designates, what sits either side of it, its sister sizes and what it is called in the other systems.

34DD UK

What the number means: The band number 34 designates an under-bust girth of 83.8-88.9 cm (33-35 in).
What the letter means: The cup letter DD is step 5 on the UK ladder: a bust-minus-band difference of 12.7-15.2 cm.
Previous cup: 34D
Next cup: 34E
Sister sizes: 32E · 36D
International equivalents: US / Canada 34DD · EU 75E · France / Spain 90E · Australia / NZ 12DD · Japan 75E
Important: A cup letter is not an absolute breast volume. The same letter names a bigger cup on a bigger band, because the cup is defined as a difference from the band and not as a quantity on its own.

The UK cup ladder in order, with the difference each rung designates
Step	Cup	Also printed as	Difference (cm)	Difference (in)	Sources agree
0	AA	—	0.0-2.5	0.00-1.00	strong
1	A	—	2.5-5.1	1.00-2.00	strong
2	B	—	5.1-7.6	2.00-3.00	strong
3	C	—	7.6-10.2	3.00-4.00	strong
4	D	—	10.2-12.7	4.00-5.00	strong
5	DD (yours)	—	12.7-15.2	5.00-6.00	strong
6	E	—	15.2-17.8	6.00-7.00	strong
7	F	—	17.8-20.3	7.00-8.00	strong
8	FF	—	20.3-22.9	8.00-9.00	strong
9	G	—	22.9-25.4	9.00-10.00	strong
10	GG	—	25.4-27.9	10.00-11.00	moderate
11	H	—	27.9-30.5	11.00-12.00	moderate
12	HH	—	30.5-33.0	12.00-13.00	moderate
13	J	—	33.0-35.6	13.00-14.00	moderate
14	JJ	—	35.6-38.1	14.00-15.00	moderate
15	K	—	38.1-40.6	15.00-16.00	moderate
16	KK	—	40.6-43.2	16.00-17.00	variable
17	L	—	43.2-45.7	17.00-18.00	variable

The basis for this ladder is bust girth minus the band number. That is a real structural difference between the inch systems and the centimetre systems, and it is one reason the same body gets different letters in different countries.

Every ladder side by side

Every supported cup ladder side by side, aligned by rung. A dash means that system has no rung there and no letter is invented for it.
Rung	UK	US	EU	FR	AU	JP
-1	—	—	—	—	—	AAA
0	AA	AA	AA	AA	AA	AA
1	A	A	A	A	A	A
2	B	B	B	B	B	B
3	C	C	C	C	C	C
4	D	D	D	D	D	D
5	DD	DD (E)	E	E	DD (E)	E
6	E	DDD (F)	F	F	E (DDD)	F
7	F	DDDD (G/4D)	G	G	F	G
8	FF	H (5D)	H	H	FF (G)	H
9	G	I	I	I	G	I
10	GG	J	J	J	GG	J
11	H	K	K	K	H	—
12	HH	—	L	L	HH	—
13	J	—	—	—	J	—
14	JJ	—	—	—	JJ	—
15	K	—	—	—	K	—
16	KK	—	—	—	—	—
17	L	—	—	—	—	—

How bra sizes work

The number designates an interval of under-bust girths. On the inch ladders a band of 34 designates roughly 33 to 35 inches. On the centimetre ladders a band of 75 designates 72.5 to 77.5 centimetres. EN 13402-3:2017 sets out exactly this principle for European size labelling: a designation names an interval of body measurements, and the interval width is part of the designation.

The letter designates an interval of differences. It names how much bigger the bust girth is than the reference that system takes the cup from, measured in that system's own step: one inch in the UK, US and Australia, two centimetres in Europe, 2.5 centimetres in Japan.

A cup letter is not an absolute breast volume. The same letter names a bigger cup on a bigger band, because the cup is defined as a difference from the band and not as a quantity on its own. A 30D and a 38D do not hold the same volume, and neither does a UK D and a Japanese D. This is the single most useful thing to know about bra sizing, and it is why this page never treats a letter as a fact about a body.

What is the smallest or largest bra size?

There is no universal smallest or largest bra size across all manufacturers and sizing systems. What follows is only the range this calculator’s verified datasets document, named per system.

The smallest and largest sizes represented in this calculator's verified datasets, named per system. These are the limits of what is documented here, not the limits of what exists.
System	Smallest represented	Largest represented	Under-bust span (cm)
UK	26AA	50L	63.5–129.5
US / Canada	26AA	50K	63.5–129.5
EU	55AA	110L	52.5–112.5
France / Spain	70AA	125L	52.5–112.5
Australia / NZ	4AA	28K	63.5–129.5
Japan	60AAA	105J	57.5–107.5

How to measure your bra size

Take every reading at the end of a relaxed breath OUT, standing upright with arms down. McGhee and Steele (2006) measured the same women at end inspiration and at relaxed expiration and found the calculated band size rose and the calculated cup size fell when the measurement was taken at inspiration, so the breathing state is part of the measurement, not a detail.

Snug against the body without compressing it, tape horizontal all the way round and level at the back.

Snug under-bust

How: Directly under the bust, in the crease where the breast tissue ends, tape firm and level.

Why: This is the band measurement. It is used raw — nothing is added to it.

Described in words: A front view of a torso with a horizontal tape drawn tight around the ribcage immediately below the bust, level all the way round.

Standing bust

How: Across the fullest part of the bust, standing upright, tape horizontal and not compressing.

Why: The reference bust reading every system's cup rule is written against.

Described in words: The same torso, standing upright, with a horizontal tape drawn across the fullest part of the bust without compressing it.

Leaning bust (advanced)

How: Bend forward from the hips to roughly 90 degrees and let the breast tissue hang; measure across the fullest part.

Why: Standing alone can under-read the bust when tissue sits low. The leaning reading usually sits at or above the standing one, and the gap between them is real information about how the tissue is distributed.

Described in words: The torso tilted forward from the hips so the tissue hangs away from the chest, with the tape across the fullest point of the hanging tissue.

Lying bust (advanced)

How: Lie flat on your back and measure across the fullest part of the bust.

Why: Lying spreads the tissue and usually gives the smallest of the three bust readings. Together the three bracket the range a bra actually has to work across.

Described in words: The torso seen flattened, as when lying on the back, with the tape across the fullest part of the spread tissue.

Advanced measurement — what the extra four readings are for

In the worked advanced example on this page the six readings support 34D–34E, with measurement stability graded Low. That is the point of the mode: the spread between a loose and a tight under-bust reading, and between a standing, leaning and lying bust reading, is real information about how much your own measurement moves — and it is reported instead of being averaged away.

Where a second reading is supplied for a measurement, the engine uses the arithmetic mean of the two readings and records the averaging step explicitly in the calculation receipt. A second reading is never silently discarded and never silently preferred.

Why another calculator may give you a different size

Almost all of the difference between bra size calculators comes down to one decision: what to do with the raw under-bust reading. This page uses it as it is. A large family of older charts adds four inches to it, or five if it is odd. From the same two numbers those two choices land on different bands and, because the cup is a difference from the band, on very different letters.

What a different method would have said about the same two measurements
Method	Result	Status
Snug under-bust, nearest step on the ladder	34DD	Used for the result on this page
Snug under-bust, rounded up to the next step	34DD	Documented alternative; counted in the source-agreement grade
Legacy additive method (add four or five inches)	38A	Legacy / traditional. Excluded from the result and from the agreement grade.

Why it is excluded: White and Scurr (2012) found the traditional method over-estimates band size and under-estimates cup size, with the discrepancy largest for larger-breasted women; McGhee and Steele (2006) advocate deriving the band from the raw under-bust measurement.

The other reasons results differ

Raw under-bust versus additive methods. The choice above. McGhee and Steele (2006) advocate deriving the band from the raw under-bust measurement; White and Scurr (2012) found the traditional method over-estimates band size and under-estimates cup size, most severely for larger-breasted women.
Manufacturer-specific charts. A brand's chart describes that brand's garments. It is not a claim about sizing in general, and two brands' charts can disagree without either being wrong.
Different cup progressions. The UK inserts E, F and FF where the United States repeats the letter as DDD and DDDD. Europe runs a single letter series with no double letters. Japan starts a rung lower, at AAA. The same rung genuinely has different names.
Different rounding. Rounding to the nearest rung and rounding up to the next one are both published fitting instructions, and they disagree about half the time. Both are computed here and the disagreement is what the source-agreement grade reports.
Fit-based correction. A fitter adjusts the number after seeing the bra on the body. A calculator cannot do that, which is why this one hands you a fit check instead of pretending to.

Why the right size can still feel wrong

A correct nominal size does not guarantee compatible bra geometry. Two bodies with identical girths can need differently shaped cups at the same size, and none of the following is standardised or set by the size number:

Projection: How far the tissue stands out from the chest. Two bodies with the same girths and different projection need differently shaped cups at the same nominal size.
Cup depth: How deep the cup is built at its fullest point. A shallow cup wrinkles on projected tissue; a deep cup gapes on shallow tissue. Neither is a volume error.
Cup width: How wide the cup is at the base. Too narrow and tissue is left outside at the side; too wide and the cup sits out under the arm.
Wire width: The wire has to sit around the breast root, not on it. Wire width is set by the style, and it does not move reliably when you change cup size.
Breast root: The footprint where the tissue meets the chest wall. A narrow root in a wide wire and a wide root in a narrow wire both hurt, at any size.
Fullness distribution: Whether the volume sits higher or lower on the root. This is what decides whether a balcony, a plunge or a full cup works, at the same size.
Bra style: Balcony, plunge, moulded, seamed, sports, wireless — each makes different assumptions about all of the above.
Stretch and material: A stretch cup forgives a size error; a rigid seamed cup does not. Two bras of the same nominal size in different fabrics are not the same garment.

This is why the fit check can return “possibly a shape or style mismatch” and decline to change your size. Chen, LaBat and Bye (2010) examined physical characteristics related to bra fit beyond the two girths a size is built from; no shape category is assigned to anyone by this calculator.

Methodology

This calculator estimates a starting bra size. It does not determine a universally correct size.

Every figure on this page comes from one deterministic engine shared by the server, the browser and the automated tests. Two measurements are converted to millimetres with the exact definition 1 in = 2.54 cm and are never rounded before a rule runs. The snug under-bust girth is placed on the selected system's own band ladder and the difference that system defines is placed on its own cup ladder; the legacy add-four method is computed for comparison only and is excluded from every recommendation. Two uncertainties are reported separately and never as percentages: measurement stability, from the spread between your own readings and your distance from an interval boundary, and source agreement, from how far apart the independent documented methods land. Every ladder, interval and grade threshold is read from the versioned bra-size-systems dataset; every rule cites a source id that resolves in the bra-size-source-charts registry.

Four different things, deliberately kept apart

Body measurement: A tape circumference in millimetres. Objective, reproducible to within how you hold the tape and when you breathe, and the only physical input this page has.
Nominal bra size: Which rung of a published ladder that measurement falls on. A convention, not a property of your body — and a different convention in each country.
Brand-specific fit: What a particular manufacturer builds at that nominal size. Cup depth, wire width, strap placement and fabric are set here, and none of them is standardised.
Verified physical fit: Whether the garment actually works on the body, assessed against observable criteria. Only this last one is a fit. This page can reach the first two, help you check the fourth, and says nothing it cannot support about the third.

The pipeline, step by step

Input measurements — Two readings are required: a snug under-bust girth and a standing bust girth, both at the end of a relaxed breath out. Four further readings — loose and tight under-bust, leaning and lying bust — are optional and are used only to grade stability, never to override the two reference readings.
Unit normalization — All classification arithmetic runs on unrounded millimetres. Inputs in centimetres are multiplied by 10 and inputs in inches by exactly 25.4; nothing is rounded before a band or cup interval is decided. Rounding happens only in the view layer, and the receipt records the unrounded values it was given.
Measure twice and average — Where a second reading is supplied for a measurement, the engine uses the arithmetic mean of the two readings and records the averaging step explicitly in the calculation receipt. A second reading is never silently discarded and never silently preferred.
Source selection — Every ladder, interval and rule is read from the versioned bra-size-systems dataset, and every rule cites source ids that resolve in the bra-size-source-charts registry. A rule with no resolvable source throws at build time rather than rendering.
Candidate generation — Each documented, non-legacy band-derivation method registered for the selected system is run on the reference pair, producing one candidate each. Separately, every combination of the readings you supplied is run through the primary method.
Consensus — Source agreement grades how far apart the method candidates land: Strong when they coincide, Moderate when they are one step apart, Variable beyond that, and Not available when fewer than two independent methods exist for that system. No estimate is substituted for Not available.
Stability — Measurement stability grades how far apart your own readings land, and whether either reading sits within a quarter of an inch of an interval boundary. High, Moderate or Low — never a percentage.
Conversion — Two independent bridges are computed. The label bridge is the conversion manufacturers print, expressed through a common band rank and cup label rank. The body bridge applies the target system’s own measurement rule to the body the source size designates. Where they disagree by more than one step, both are shown and the cause is named.
Sister sizing — One band down with one cup up, or one band up with one cup down, read from the selected system’s own ladder. Sister sizing preserves nominal cup volume approximately within one convention; it guarantees nothing about wire width, cup depth or construction.
Fit diagnosis — Observable fit criteria are grouped by bra component and scored into five signal dimensions. The first matching rule in the versioned rule list is applied. Underwire answers are read only when the bra is wired. Symptoms marked as insufficient on their own can never move a size by themselves.
Rounding — Rounding happens only in the view layer. Every band and cup decision is taken on unrounded millimetres, and the receipt records the unrounded values the engine was given.
Limitations — Listed in full below, including the systems this calculator refuses to convert into.

Assumptions

Every reading is a tape circumference taken on a bare or lightly clothed body, tape horizontal and level at the back, at the end of a relaxed breath out.
The snug under-bust reading is used raw. Nothing is added to it before it is placed on a band ladder.
A band designates an interval of under-bust girths and a cup designates an interval of bust-to-band differences; both are treated as intervals throughout, never as point values.
Sister sizing preserves the nominal cup volume approximately, within one system's convention only.
The fit check reads answers about a garment, not about a body, and assumes the bra is described on the hook it is normally worn on.

Limitations

This calculator estimates a starting bra size. It does not determine a universally correct size, and it cannot verify that any garment will fit.
The band and cup ladders are documented labelling conventions, not quotations from a standard: the normative text of ISO 8559-1:2017, EN 13402-3:2017 and JIS L 4006:1998 is paywalled and was not read.
The published cross-system label conversion and each system's own measurement rule disagree, often by about two European band steps, because published charts carry the legacy additive band convention. Both answers are shown; neither is declared correct.
United States cup letters above DDD, and Australian and New Zealand letters above D, are genuinely inconsistent between manufacturers. Those rungs are graded variable and carry their alternative letters instead of being given one confident answer.
China, Italy, South Korea, Brazil and India are declared unsupported. No conversion into them is offered, because no defensible rule for them could be documented here.
Nothing on this page is a medical, diagnostic or clinical assessment, and no claim is made about pain, posture or breast health.

Review status

No clinical or professional bra-fitting review has been performed on this page, and none is claimed. What has been verified, on 2026-08-10 by an automated check: every DOI cited resolves and its bibliographic record matches, and the catalogue records of ISO 8559-1:2017, EN 13402-3:2017 and JIS L 4006:1998 match their entries. What has not been verified: the paywalled normative text of those three standards was not read, so the band and cup ladders are recorded as documented conventions rather than as quotations from any standard.

Dataset versions in use: bra-size-systems v1.0.0 (verified: no), bra-size-source-charts v1.0.0 (verified: yes), bra-fit-criteria v1.0.0 (verified: no). Engine: bra-size-engine v1.0.0.

A starting size, not a verdict

This calculator estimates a starting bra size. It does not determine a universally correct size.

Two measurements can tell you which rung of a published ladder your body falls on. They cannot tell you whether a particular garment, cut for particular assumptions about depth, width and projection, will fit you. Those are different questions, and the second one is answered by putting a bra on.

McGhee and Steele (2010) found that the sizes produced by self-selection and by standard measurement systems both differed significantly from the size professional fit criteria produced. The honest response to that is not a more confident number — it is a number with a range around it and a fit check attached.

A size is an interval, not a point

Every band and every cup on this page names a range of body measurements. A band of 34 designates an under-bust girth of about 33 to 35 inches; a UK D cup designates a bust-to-band difference of 4 to 5 inches. EN 13402-3:2017 sets out exactly this principle for European size labelling: a designation names an interval, and the interval width is part of the designation.

That is why the result carries a measurement-supported range rather than a single size, and why sitting a quarter of an inch from an interval edge is reported to you instead of being rounded away.

Two uncertainties, kept apart

Measurement stability answers: do YOUR OWN readings agree? It comes from the spread between the readings you gave and from how close you sit to an interval boundary.

Source agreement answers: do the DOCUMENTED METHODS agree, for one fixed pair of measurements? It comes from comparing the independent band-derivation methods registered for the system you chose.

Neither is ever expressed as a percentage. Neither is a sample from any distribution, so a percentage would be a decoration rather than a measurement.

Why the legacy add-four method is not used here

A very large number of charts and calculators derive the band by adding four inches to the under-bust reading, or five if it is odd. This page computes that answer — you can see it in the comparison section — but never uses it for a recommendation.

White and Scurr (2012) found the traditional method differed significantly from best fit, over-estimating band size and under-estimating cup size, with the discrepancy largest for larger-breasted women. McGhee and Steele (2006) advocate deriving the band from the raw under-bust measurement.

That is the whole reason another calculator can hand you a band two sizes larger than this one does.

Size is not shape

A correct nominal size does not guarantee compatible bra geometry. Projection, cup depth, cup width, wire width, breast root width, where the fullness sits, the style and the fabric are all set by the garment and none of them is standardised.

The fit check on this page is built to separate these two things: it will tell you when what you are seeing is more likely a shape or style mismatch than a size error, and it will decline to change your size on that evidence.

Sources and evidence

Every rule, ladder and fit criterion on this page cites at least one record below. Each record states what it supports and what it does not, so a study is never quietly stretched to cover a formula it does not validate.

Authority tiers. Tier 1: International or national standards body, or a peer-reviewed primary study published in an indexed journal. Tier 2: Peer-reviewed secondary or applied study, or a primary technical source that is authoritative for one system only. Tier 3: Documented labelling convention with no single owning authority, or an explicitly disclosed CalcDomain modelling decision.

Verification statuses. doi-record-verified — The DOI resolves and the bibliographic record returned by Crossref (and, where indexed, Europe PMC) matches this entry field by field. Where an abstract was returned it was read before the support statements below were written. Full text was not necessarily read. catalogue-record-verified — The standard's catalogue record (number, title, edition year, published scope) was verified against the issuing body or an authorised distributor. The normative text is paywalled and was NOT read; nothing numeric is reproduced from it. convention-documented-no-single-authority — A labelling convention that is published consistently by many independent manufacturers and size guides but is owned by no standards body. Recorded as a convention, never as a standard. declared-own-work — A CalcDomain modelling decision, fully disclosed. Not external evidence.

McGhee DE, Steele JR. How do respiratory state and measurement method affect bra size calculations? Br J Sports Med. 2006;40(12):970-974.

Biomechanics Research Laboratory, University of Wollongong — published in British Journal of Sports Medicine (BMJ) · 2006 · DOI 10.1136/bjsm.2005.025171 · Tier 1 · doi-record-verified · reviewed 2026-08-10 · bjsm-2006-40-12-970@1.0.0

What it supports:

That the respiratory state at which a bra measurement is taken materially changes the calculated size: measuring at end inspiration increased the calculated band size and decreased the calculated cup size compared with relaxed expiration.
That the measurement method itself changes the calculated size, and that a standardised respiratory state must therefore be specified as part of any measurement protocol.
That deriving the band from the RAW under-bust measurement is an approach the authors advocate, rather than from an additive correction to it.
That two readings of the same body can legitimately differ, which is why this tool offers a measure-twice-and-average step and reports measurement stability instead of a single confident number.

What it does not support:

It does not define, validate or endorse any cup-letter ladder, band ladder or size chart.
It does not validate any conversion between sizing systems.
It does not establish a numeric tolerance, a confidence percentage or a probability for any size estimate.
The study population was 16 large-breasted women; it is not a population-representative anthropometric survey.

Measurement ranges: Not applicable — a methodological study, not a size chart.

The single most load-bearing source on this page. It is why the tool asks for a SNUG under-bust taken at the end of a relaxed breath out, why it never adds four or five inches to that reading, and why it treats a difference between two of your own readings as information rather than noise.

White J, Scurr J. Evaluation of professional bra fitting criteria for bra selection and fitting in the UK. Ergonomics. 2012;55(6):704-711.

Department of Sport and Exercise Science, University of Portsmouth — published in Ergonomics (Taylor & Francis) · 2012 · DOI 10.1080/00140139.2011.647096 · Tier 1 · doi-record-verified · reviewed 2026-08-10 · ergonomics-2012-55-6-704@1.0.0

What it supports:

That professional bra-fitting criteria — observable checks on the band, cups, underwire, front band and straps — are a distinct and better-performing basis for selecting a bra than a tape-measure formula alone.
That the traditional tape-measure method differs significantly from best fit, over-estimating band size and under-estimating cup size, and that the discrepancy is largest for larger-breasted women.
That the practical recommendation is to teach people to assess fit rather than to chase an absolute size number — which is why this page pairs every estimate with a fit check and calls the estimate a starting size.

What it does not support:

It does not publish a size chart, a cup ladder or a conversion table.
It does not license any particular arithmetic rule for deriving a band or a cup from a tape measurement.
It does not support turning any single fit symptom into an automatic size change; the criteria are assessed together.

Measurement ranges: Not applicable — a fit-criteria evaluation, not a size chart.

The evidential basis for the whole "Check my current bra" mode and for the refusal to present the legacy add-four/add-five method as a primary algorithm.

McGhee DE, Steele JR. Optimising breast support in female patients through correct bra fit. A cross-sectional study. J Sci Med Sport. 2010;13(6):568-572.

Biomechanics Research Laboratory, University of Wollongong — published in Journal of Science and Medicine in Sport (Elsevier) · 2010 · DOI 10.1016/j.jsams.2010.03.003 · Tier 1 · doi-record-verified · reviewed 2026-08-10 · jsams-2010-13-6-568@1.0.0

What it supports:

That ill-fitting bras are common: 85% of the 104 participants assessed were wearing a bra that did not fit by professional fit criteria.
That sizes arrived at by self-selection and by standard measurement systems differed significantly from the size arrived at by professional fit criteria.
That a calculated size and a verified fit are different things — the distinction this page draws between a nominal size and a physically verified fit.

What it does not support:

It does not say that any particular calculator, chart or formula is correct.
It does not give a per-symptom diagnostic rule.
The 85% figure describes that study's participants; it is not presented here as a general population rate and is not used in any calculation.

Measurement ranges: Not applicable — a cross-sectional fit study, not a size chart.

Cited on the page for one claim only: that the gap between a measured size and a fitting size is large and common enough that a calculator must not present its output as a settled answer.

Greenbaum AR, Heslop T, Morris J, Dunn KW. An investigation of the suitability of bra fit in women referred for reduction mammaplasty. Br J Plast Surg. 2003;56(3):230-236.

Department of Plastic Surgery, Wythenshawe Hospital, Manchester — published in British Journal of Plastic Surgery (Elsevier) · 2003 · DOI 10.1016/S0007-1226(03)00122-X · Tier 2 · doi-record-verified · reviewed 2026-08-10 · bjps-2003-56-3-230@1.0.0

What it supports:

That the direction of sizing error is systematic rather than random: in this referred population, band measurements were under-estimated by a mean of four inches and cup size over-estimated by about three sizes.
That a too-large band combined with a too-small cup is the characteristic failure mode a fit check should look for first.

What it does not support:

It does not generalise to the whole population: all 103 participants were women referred for reduction mammaplasty.
It does not validate a replacement formula.
The four-inch figure is an observed mean error in that cohort. It is NOT used anywhere in this engine as a correction, an offset or a rule.

Measurement ranges: Not applicable — a clinical audit, not a size chart.

Used only to explain WHY the band is checked before the cup in the fit diagnosis, and never as a numeric adjustment.

Coltman CE, Steele JR, McGhee DE. Which Bra Components Contribute to Incorrect Bra Fit in Women Across a Range of Breast Sizes? Cloth Text Res J. 2018;36(2):78-90.

Biomechanics Research Laboratory, University of Wollongong — published in Clothing and Textiles Research Journal (SAGE) · 2017 · DOI 10.1177/0887302X17743814 · Tier 2 · doi-record-verified · reviewed 2026-08-10 · ctrj-2018-36-2-78@1.0.0

What it supports:

That bra fit is properly assessed component by component — cups, front band, underwire, straps and band are separate failure surfaces, not one score.
That across 309 women the highest prevalence of incorrect fit was in the cups, the front band and the straps.
That front band, underwire and strap fit vary significantly with breast size, which is why this tool never treats a strap or gore symptom on its own as evidence for a size change.

What it does not support:

It does not publish a decision rule mapping a symptom to a size change.
It does not rank the interventions this page offers.
It does not establish that any component symptom is sufficient on its own to determine a size.

Measurement ranges: Not applicable — a component-level fit prevalence study.

The reason bra-fit-criteria.json is split into band, cup, underwire, front-band/gore and strap groups rather than one flat checklist.

Chen C-M, LaBat K, Bye E. Physical characteristics related to bra fit. Ergonomics. 2010;53(4):514-524.

College of Design, University of Minnesota — published in Ergonomics (Taylor & Francis) · 2010 · DOI 10.1080/00140130903490684 · Tier 2 · doi-record-verified · reviewed 2026-08-10 · ergonomics-2010-53-4-514@1.0.0

What it supports:

That physical characteristics beyond the two girth measurements a size is built from are related to whether a bra fits.
The central claim of the "Why the right size can still feel wrong" section: a correct nominal size does not guarantee compatible bra geometry.

What it does not support:

It does not provide a shape taxonomy this tool could classify you into, and this tool does not attempt one.
It does not license any numeric adjustment based on shape.

Measurement ranges: Not applicable.

Supports the size-versus-shape distinction only. No shape category is assigned to anyone by this calculator.

McGhee DE, Steele JR. Breast volume and bra size. Int J Cloth Sci Technol. 2011;23(5):351-360.

University of Wollongong — published in International Journal of Clothing Science and Technology (Emerald) · 2011 · DOI 10.1108/09556221111166284 · Tier 2 · doi-record-verified · reviewed 2026-08-10 · ijcst-2011-23-5-351@1.0.0

What it supports:

That the relationship between measured breast volume and bra size designation is a subject of primary research rather than a settled identity — the published basis for this page's statement that a cup letter is not an absolute volume.

What it does not support:

No numeric volume figure, band-to-volume table or cup-to-volume mapping is taken from this work. Only the Crossref bibliographic record was verified; the full text was not read in this environment, and no quantitative claim is attributed to it anywhere on the page.

Measurement ranges: Not used.

Deliberately carries the weakest claim of any study in this registry, because only its bibliographic record was verified.

Zheng R, Yu W, Fan J. Development of a new Chinese bra sizing system based on breast anthropometric measurements. Int J Ind Ergon. 2007;37(8):697-705.

Institute of Textiles and Clothing, The Hong Kong Polytechnic University — published in International Journal of Industrial Ergonomics (Elsevier) · 2007 · DOI 10.1016/j.ergon.2007.05.008 · Tier 2 · doi-record-verified · reviewed 2026-08-10 · ijie-2007-37-8-697@1.0.0

What it supports:

That a bra sizing system is a constructed convention built on a population's anthropometric data, not a physical constant — the reason two systems can label the same body differently without either being wrong.
The decision to leave a Chinese system UNSUPPORTED in this calculator rather than approximate one: the published work itself proposes a new system precisely because the existing mapping was inadequate for that population.

What it does not support:

No band ladder, cup ladder or conversion is taken from this work. The Chinese system is declared unsupported on this page.
It does not validate any of the systems this calculator does support.

Measurement ranges: Not used.

Cited to justify a refusal, not a number.

ISO 8559-1:2017 — Size designation of clothes — Part 1: Anthropometric definitions for body measurement

ISO (International Organization for Standardization), technical committee ISO/TC 133 · 2017 · Tier 1 · catalogue-record-verified · reviewed 2026-08-10 · iso-8559-1-2017-catalogue@1.0.0

What it supports:

That the body measurements a garment size is designated from are themselves standardised definitions with a defined anatomical basis and a defined way of being taken, rather than informal instructions.
The methodological position taken here: the measurement protocol is part of the result, and a size quoted without the protocol that produced it is incomplete.

What it does not support:

The normative text is paywalled and was not read in this environment. No definition is quoted from it, no measurement value is reproduced from it, and no cup or band ladder is attributed to it.
It does not designate bra sizes and contains no cup-letter system.

Measurement ranges: Not reproduced.

Catalogue record verified 2026-08-10: number, exact title, 2017 edition and published scope. Cited for methodology only.

EN 13402-3:2017 — Size designation of clothes — Part 3: Size labelling based on body measurements and intervals

CEN (European Committee for Standardization) · 2017 · Tier 1 · catalogue-record-verified · reviewed 2026-08-10 · en-13402-3-2017-catalogue@1.0.0

What it supports:

The principle this whole engine is built on: a size designation names an INTERVAL of body measurements in centimetres, not a point value, and the interval width is part of the designation.
That European size labelling is expressed from primary body dimensions in centimetres, which is why the European band ladder in this calculator is a centimetre ladder derived from the under-bust girth rather than a converted inch number.

What it does not support:

The normative text is paywalled and was not read in this environment. No table, interval scheme or annex value is reproduced from it.
The specific European five-centimetre band ladder and the two-centimetre cup progression used by this calculator are recorded as a DOCUMENTED CONVENTION (see eu-band-cup-convention), not as a quotation from this standard.

Measurement ranges: Not reproduced.

Catalogue record verified 2026-08-10: number, exact title, 2017 edition, CEN approval and published scope. Cited for the interval principle only.

JIS L 4006:1998 — Sizing systems for foundation garments

Japanese Industrial Standards Committee / Japanese Standards Association (JSA) · 1998 · Tier 1 · catalogue-record-verified · reviewed 2026-08-10 · jis-l-4006-1998-catalogue@1.0.0

What it supports:

That Japan designates foundation-garment sizes — brassieres among them — under a national standard rather than by importing another country's ladder, which is why Japan is modelled as its own system here and not as a relabelling of the European one.

What it does not support:

The normative text is paywalled and was not read in this environment. No table is reproduced from it.
The Japanese band and cup steps used by this calculator are recorded as a DOCUMENTED CONVENTION (see jp-band-cup-convention), not as a quotation from this standard.
This calculator's Japanese ladder carries a reduced-confidence flag for exactly that reason.

Measurement ranges: Not reproduced.

Catalogue record verified 2026-08-10 against authorised distributor listings: standard number, exact English title "Sizing systems for foundation garments" and 1998 publication date.

CalcDomain bra-size modelling decisions: interval arithmetic, candidate methods, measurement stability and source agreement

CalcDomain (own work, fully disclosed) · 2026 · Tier 3 · declared-own-work · reviewed 2026-08-10 · calcdomain-bra-size-model@1.0.0

What it supports:

The decision to treat every band and cup as a measurement INTERVAL and to report an adjacent supported range rather than a bare number.
The three-state measurement-stability grade (High / Moderate / Low) and the three-state source-agreement grade (Strong / Moderate / Variable), and the rule that neither is ever expressed as a percentage or a probability.
The decision to register more than one documented band-derivation method per system and to grade their agreement, instead of presenting a single method as settled.
The decision to exclude the legacy add-four / add-five method from the primary result while still computing it for the comparison section.

What it does not support:

None of this is external evidence. It is a disclosed engineering model, and it is labelled as such wherever it appears on the page.
It confers no clinical, medical or professional-fitting authority.

Measurement ranges: Underbust 55-150 cm and bust 60-190 cm are the ranges the engine will accept; outside them it fails closed with a reason instead of extrapolating.

Every grade, interval and refusal in the engine traces to this record when it does not trace to one of the eleven external records above.

Even-inch band ladder and one-inch cup step

No single owning authority — a labelling convention published consistently by independent manufacturers and fitting guides across the United Kingdom, Ireland, the United States, Canada, Australia and New Zealand · Tier 3 · convention-documented-no-single-authority · reviewed 2026-08-10 · uk-us-band-even-inch@1.0.0

What it supports:

That band sizes in the inch-based systems run in even numbers two inches apart (28, 30, 32, 34, ...).
That one cup step corresponds to one inch of difference between the bust girth and the band number.

What it does not support:

It does not fix how the raw under-bust reading becomes the band number. That step is genuinely contested, which is why this engine registers more than one method for it and reports how well they agree.
It does not fix the cup letters above the sixth step, where manufacturers diverge.

Recorded as a convention with no owning standards body. The page says so.

Five-centimetre European band ladder and two-centimetre cup progression

No single owning authority — the centimetre band and cup convention used across continental European labelling, consistent with the interval principle of EN 13402-3:2017 · Tier 3 · convention-documented-no-single-authority · reviewed 2026-08-10 · eu-band-cup@1.0.0

What it supports:

That the European band number is the under-bust girth in centimetres placed on a five-centimetre ladder (60, 65, 70, 75, ...).
That the European cup ladder is a single-letter run with no double letters, stepping every two centimetres of bust-minus-under-bust difference.
That the French and Spanish band number is the European band number plus 15, with the same cup letters.

What it does not support:

It is not a quotation from EN 13402-3:2017; that standard's tables are paywalled and are not reproduced here.
It does not license any equivalence between a European label and an inch-system label. That equivalence is a separate, and separately graded, question.

Carries agreement grade "moderate" in the catalog because the ladder itself is consistently published but its anchor against the inch systems is not.

Five-centimetre Japanese band ladder and 2.5-centimetre cup progression

No single owning authority — the Japanese retail convention, consistent with Japan having its own foundation-garment standard (JIS L 4006:1998) · Tier 3 · convention-documented-no-single-authority · reviewed 2026-08-10 · jp-band-cup@1.0.0

What it supports:

That the Japanese band number is the under-bust girth in centimetres on a five-centimetre ladder.
That the Japanese cup ladder steps every 2.5 centimetres of bust-minus-under-bust difference and includes an AAA step below AA.

What it does not support:

It is not a quotation from JIS L 4006:1998, whose text is paywalled and was not read.
It does not license an exact equivalence between a Japanese label and any other system's label.

Carries agreement grade "variable" for cross-system label equivalence.

Published label-conversion convention: 2 inches of band ≙ 5 centimetres of band, anchored at UK/US 32 ≙ EU 70; cup letters share a common rank in which UK DD, US DD and EU E coincide

No single owning authority — the cross-system label conversion published near-identically by many independent manufacturers and size guides · Tier 3 · convention-documented-no-single-authority · reviewed 2026-08-10 · published-label-conversion@1.0.0

What it supports:

That when manufacturers print a conversion between an inch label and a centimetre label they place UK/US 30 against EU 65, 32 against 70, 34 against 75 and 36 against 80.
That in the same published convention the cup letters line up so that UK DD, US DD and EU E name one step, UK E and EU F the next, and so on.

What it does not support:

It does NOT agree with what the two systems' own measurement rules designate for the same body. The published label convention places an inch band about four inches — roughly ten centimetres, two European steps — away from where the under-bust girth alone would place it. That gap is the legacy additive band convention, and this calculator reports the disagreement rather than hiding it.
It is not a standard and no standards body publishes it.
It does not guarantee that a garment carrying the converted label will fit.

Implemented so that converting a LABEL gives the answer a shop would give, while converting a BODY gives what each system's own rule designates — and the engine shows both whenever they disagree.

Legacy additive band method (add four inches to an even under-bust reading, five to an odd one)

No single owning authority — the historical additive band method, retained here only for comparison · Tier 3 · convention-documented-no-single-authority · reviewed 2026-08-10 · legacy-additive-band@1.0.0

What it supports:

That a large family of older charts and calculators derives the band by adding four or five inches to the under-bust reading, which is why another tool can hand you a band two sizes larger than this one does.
That the published cross-system label conversion is internally consistent with this legacy convention: an inch label assigned this way sits about four inches above the raw under-bust girth, which is very nearly the ten-centimetre offset the published conversion carries.

What it does not support:

It is NOT used to produce any primary result on this page. White & Scurr (2012) found the traditional method over-estimates band size and under-estimates cup size, most severely for larger-breasted women, and McGhee & Steele (2006) advocate deriving the band from the raw under-bust measurement.
It is not endorsed here, and no claim is made that it is wrong for every body — only that the evidence available does not support using it as a default.

Computed by the engine ONLY for the comparison section, and flagged excludedFromPrimary so it can never reach a recommendation or a source-agreement grade.

Frequently asked questions

How do I calculate my bra size?

Take two measurements at the end of a relaxed breath out: the snug under-bust girth in the crease beneath the bust, and the bust girth across the fullest part. The under-bust reading is placed on your chosen system's band ladder, and the difference between the two readings is placed on that system's cup ladder. This page does that for six sizing systems at once and shows the arithmetic in the calculation receipt at #methodology. Nothing is added to the under-bust reading.

How do I measure bra size at home?

Stand upright with your arms down and a tape that is horizontal and level at the back. Measure the snug under-bust first, then the standing bust, both at the end of a relaxed breath out — McGhee and Steele (2006) found that breathing in raises the calculated band and lowers the calculated cup. The diagrams and the full protocol are at #how-to-measure-bra-size, and the measure-twice option averages two readings so a single unlucky tape pull does not decide your answer.

What is my cup size?

Your cup letter is whichever rung of your chosen system's cup ladder the difference between your bust and your band falls in. In the inch systems one rung is one inch of difference; in Europe it is two centimetres and in Japan 2.5. That is why the same body gets different letters in different systems, and it is shown side by side at #cup-size-chart.

How do bra cup sizes work?

A cup letter is a step, not a quantity. It names how much bigger the bust girth is than the band, measured in that system's own step size, so it only means anything relative to the band it sits on. The ladder, its step size and its interval boundaries are all listed at #cup-sizes-in-order.

What does the number in a bra size mean?

It designates an interval of under-bust girths. On the inch ladders a band of 34 designates roughly 33 to 35 inches; on the centimetre ladders a band of 75 designates 72.5 to 77.5 centimetres. The exact interval for every band is in the table at #bra-size-chart.

What does the letter mean?

It designates an interval of differences between your bust girth and the reference the system takes the cup from. It does not name a volume, a shape or a projection, and it is not comparable across bands. See #cup-size-chart for every interval.

Is a D cup always the same size?

No. The same letter names a bigger cup on a bigger band, because the cup is defined as a difference from the band rather than as a quantity on its own — a 30D and a 38D hold noticeably different volumes. The letter also names different steps in different systems. This is explained at #how-bra-sizes-work.

What is the difference between D and DD?

One step. On the UK and US ladders DD is one inch more of bust-to-band difference than D. Above that the two systems diverge: UK continues E, F, FF, G while the US repeats the letter as DDD and DDDD. Both ladders are printed in full, side by side, at #cup-sizes-in-order.

What are sister sizes?

Sizes with approximately the same nominal cup volume on a different band: go one band down and one cup up, or one band up and one cup down. The calculator works them out from the ladder of the system you selected rather than assuming D is always followed by DD. They are at #sister-sizes, together with the caveat that a sister size does not guarantee the same wire width, cup depth or construction.

How should a bra band fit?

Level all the way round and firm enough that it does not ride up when you raise your arms, on the loosest hook when the bra is new. If it rides up, that is the strongest single signal in the fit check at #check-your-bra-fit, and the tool responds by moving the band down one and the cup up one so the volume stays roughly where it was.

How should bra cups fit?

All the tissue inside, no spilling at the top or the side, no cutting, no empty wrinkled space. Those are four separate observations and the fit check reads them separately, because they do not all point the same way.

Why does my bra ride up?

Almost always because the band is longer than the ribcage it is on, so the weight at the front pulls the back upward. Try a tighter hook first; if it is already on the tightest hook, the fit check at #check-your-bra-fit will suggest one band down with one cup up.

Why does my bra cup gap?

A gaping or wrinkling cup has two live explanations and this tool refuses to pick one for you: the cup may hold more volume than is being filled, or it may be cut for a different tissue distribution at the same nominal size. A loose band produces the same picture by holding the cup away from the body, so the band is checked first. See #visual-fit-guide.

Why am I spilling out of my bra?

Spilling at the top, at the side, or a cup edge cutting in are all evidence that the cup does not have enough volume. With a settled band the fit check suggests the same band and one cup step up; two steps are only suggested when several independent cup observations agree and the band reports nothing.

Why doesn't the center gore touch my chest?

A floating gore has at least four documented causes — not enough cup volume, a cup that is too shallow for projecting tissue, a wire that is too narrow to sit down on the ribcage, or a chest that simply is not flat between the breasts. This tool will not convert it into an automatic cup increase; it lists the causes and what would tell them apart at #visual-fit-guide.

Are US and UK sizes the same?

The band ladders are the same and the cups agree up to DD. Above that they diverge: where the UK inserts E, F and FF, the United States repeats the letter as DDD and DDDD, and US manufacturers themselves disagree about the labels above DDD. Every affected rung is graded and carries its alternative letters at #cup-sizes-in-order.

How do I convert US to UK?

Use the converter at #bra-size-conversion. The band number is unchanged and the cup letter is remapped through its rung on the ladder, so US DDD becomes UK E rather than being renamed arbitrarily. The converter also shows what each system's own measurement rule would designate for the same body, and grades how far apart the two answers are.

How do I convert to EU sizing?

The converter maps the label the way manufacturers' own charts do: inch band 32 against EU 70, 34 against 75, and cup letters aligned by rung so UK DD becomes EU E. It then does something most converters do not — it also applies EU sizing's own measurement rule to the body your size designates, and tells you when the two disagree and why. See #why-your-size-may-vary.

Should I measure in inches or cm?

Either. Every reading is converted to millimetres with the exact definition 1 in = 2.54 cm before any rule runs, and nothing is rounded until the result is displayed, so the two units cannot give different answers for the same body.

Why do calculators give different results?

Mostly because of one decision: what to do with the raw under-bust reading. This calculator uses it as it is. A very large number of older charts add four inches to it, or five if it is odd, which typically lands two band sizes higher and several cup letters lower. The section at #why-your-size-may-vary computes both from your own numbers so you can see the gap rather than take it on trust.

Can two brands fit differently in the same size?

Yes, routinely. Cup depth, cup width, wire width, strap placement, seam construction and fabric stretch are all set by the style, not by the size number, and none of them is standardised. #why-your-size-may-vary explains which of them to suspect from what you are seeing.

How accurate is a bra size calculator?

It is accurate about arithmetic and silent about fit. McGhee and Steele (2010) found 85% of the women they assessed were wearing a bra that did not fit by professional criteria, and that sizes from standard measurement systems differed significantly from the size professional fit criteria produced. That is why this page reports a starting size with a range, grades how stable your measurements are and how much the documented methods agree, and then asks you to check the fit. See #accuracy.

How often should I remeasure?

Whenever your band stops holding on its tightest hook, after a change in weight, during and after pregnancy, or when a bra that used to work stops working. There is no evidence-based interval to quote, so none is quoted here.

About this page

Written and maintained by Ugo Candido. Last reviewed August 10, 2026.

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Reviewed according to the CalcDomain Editorial Policy & Calculator Methodology. We document formulas, edge cases, sources, update dates, and correction paths for calculator pages.

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