Ideal Weight Calculator: Compare Your Healthy Range and IBW Formulas

There is no single number. For adults, screening guidance maps each height to a reference range — every weight with a BMI from 18.5 up to, but not including, 25. This tool shows that range in kilograms and pounds, plus the exact weight at any target BMI you pick inside it. Where in the range is reasonable for you depends on factors a calculator cannot see.

The adult screening reference range used here runs from BMI 18.5 (inclusive) up to BMI 25 (exclusive), read from the bound CDC-sourced dataset. Below 18.5 screens as underweight, 25 to under 30 as overweight, and 30 or above as obesity, in three classes.

No. The upper boundary is exclusive: a BMI of exactly 25.0 screens as overweight, while 24.99 screens inside the reference range. The tool classifies on the unrounded value so a displayed 25.0 is never silently placed on the wrong side.

Because the underlying evidence defines an interval of screening-normal weights, not a point. Single-number answers come from historical formulas that disagree with each other by several kilograms at the same height — which is exactly what the comparison table shows.

No. For adults, BMI is weight in kilograms divided by height in metres squared for everyone, and the adult screening categories are the same for women and men. Only some historical ideal-body-weight formulas use different constants by sex, which is why that choice exists as a separate, optional selector.

Devine, Robinson, Miller and Hamwi were published with separate male and female constant sets, so computing them requires choosing one. Skipping the choice skips only those formulas: BMI, the reference range and the waist-to-height ratio are unaffected.

Devine (1974) estimates 50.0 kg plus 2.3 kg per inch over 5 ft with male constants, and 45.5 kg plus 2.3 kg per inch over 5 ft with female constants. It was proposed for estimating gentamicin dosing weight, and later became the most widely used ideal-body-weight equation in pharmacokinetics.

Hamwi (1964) is a bedside rule from diabetes practice: 106 lb plus 6 lb per inch over 5 ft with male constants, and 100 lb plus 5 lb per inch over 5 ft with female constants. This tool computes it in its original pounds and converts with the exact factor 1 lb = 0.45359237 kg.

Both are 1983 revisions of the dosing-weight idea. Robinson uses 52.0 kg plus 1.9 kg per inch over 5 ft (male constants) and 49.0 kg plus 1.7 kg (female constants); Miller uses 56.2 kg plus 1.41 kg (male constants) and 53.1 kg plus 1.36 kg (female constants). At the same height they can differ from Devine by several kilograms.

Peterson (2016) is a BMI-based equation — in metric form, 2.2 × targetBMI + 3.5 × targetBMI × (height in metres − 1.5) — published as a single replacement for the inconsistent legacy formulas. Because it is built around BMI, it tracks the exact target-BMI weight closely at every height and needs no sex-specific constants.

Each was fitted to a different dataset, era and purpose — dosing estimation, actuarial tables, bedside arithmetic. At 182 cm with male constants the spread between the lowest and highest of the five is roughly 7 kg. The disagreement is a feature of history, not an error in the calculator.

None of them is an individualized answer. If you want a single modern reference, the Peterson equation is the only one designed around BMI, and the exact target-BMI weight is the cleanest mathematical statement of the same idea. The legacy formulas are shown for context and for their continuing role in drug-dosing conventions.

It is the weight whose BMI equals 22 at your height — an illustrative point near the middle of the adult reference range, computed as 22 × height². It is a default for comparison, not a goal; you can move the target BMI anywhere from 18.5 to 24.9.

Directly from the BMI definition: weight in kilograms equals targetBMI × height in metres squared. The implied BMI of that exact weight equals the target to floating-point precision, which the automated tests verify.

No. None of the five implemented formulas takes age as an input, and this tool never silently alters a formula by age. Age matters only for routing: under-20 visitors are not interpreted with adult categories, and visitors 65 or older see an added caution note with unchanged math.

For ages 2–19, BMI must be interpreted with sex- and age-specific percentiles from pediatric growth charts, and the bound routing dataset prohibits falling back to adult categories. This page carries no percentile tables, so it declines to classify anyone under 20 rather than misclassify them.

The math is identical, and the tool shows it unchanged. It adds a caution: in older adults, the weight range associated with the lowest health risk may sit differently than the standard adult reference range, and unintentional weight loss matters clinically — so weight goals in later life belong in a clinical conversation.

Waist circumference divided by height, in the same units. It is a simple screening signal for central adiposity — where weight is carried — which BMI alone cannot see. A memorable boundary is 0.5: keeping the waist under half of height.

The bound NICE-sourced dataset: 0.4 to under 0.5 screens as healthy central adiposity, 0.5 to under 0.6 as increased central adiposity, and 0.6 or above as high central adiposity. Boundaries are applied on the unrounded ratio.

The NICE guidance applies its standard central-adiposity classification alongside BMI only when BMI is below 35. At 35 or above the tool still shows the ratio itself but withholds the standard band, matching the guideline's applicability condition.

It falls below the classified reference interval: the NICE bands start at 0.4, so the tool reports the ratio without assigning a screening band rather than inventing one. It is not automatically a problem or an achievement — it is simply outside the classified interval.

No. BMI-based screening references do not apply during pregnancy, and weight expectations in pregnancy are managed clinically. The tool states this limitation next to its results rather than attempting any adjustment.

Poorly. BMI cannot distinguish muscle from fat, so a muscular adult can screen above the reference range while carrying little body fat. The waist-to-height ratio helps a bit as a distribution signal, but body-composition assessment is out of scope here — deliberately.

Adjusted body weight is a dosing construct that starts from an ideal-body-weight estimate and adds a fraction of the difference to actual weight. The fraction depends on the clinical protocol and the drug involved, so there is no universal factor a general-purpose page could honestly apply. This tool explains the concept and stops there.

Average weight is a description of a population; the reference range is a screening interval from health guidance. In many countries the average adult sits above the reference range, so matching the average is not evidence of anything. This tool never uses averages as targets.

Exact by definition: 1 inch = 2.54 cm and 1 pound = 0.45359237 kg, the international definitions. Every input is converted to SI before calculation, so entering the same height in metric or US units produces the same result to floating-point tolerance.

No. Height, weight, waist and every other input stay in your browser. They are never sent to a server, never included in analytics events, and never written into the page URL.

Neither. Every output is a population-level screening reference. It does not measure body composition, it does not diagnose any condition, and it does not replace evaluation by a clinician who can see the whole picture.