Millimeters to Inches Converter

Instantly convert millimeters (mm) to inches (in) with a responsive calculator that shows decimals and friendly fractions.

Type either value to update the conversion instantly. Use Calculate if you prefer explicit refresh after entering a measurement.

Millimeters (mm)

Inches (decimal)

Fractional inches

Decimal inches

0.000000

Fractional inches 0"

Millimeter equivalent 0 mm

Conversion factor 1 in = 25.4 mm

How to use

Provide whichever measurement you have (either millimeters or inches) and the interface keeps both fields aligned while showing the decimal and fraction equivalents.

Work in millimeters when precision matters; the result appears automatically in decimal inches.
Use the inches input to confirm large or fractional measurements and see the equivalent in millimeters.
Press Calculate after typing to ensure the results card reflects the latest entry, especially when pasting values.
Reset clears both fields and restores the default 10 mm example so you can start fresh.

Formulas

1 inch is defined as exactly 25.4 millimeters.

Decimal conversion from millimeters to inches: inches = millimeters × 0.0393700787

Decimal conversion from inches to millimeters: millimeters = inches × 25.4

Citations

Changelog

Version 1.5.0 – Aligned layout with canonical hero requirements and added deterministic parse/validate/compute/update flow.

Full original guide (expanded)

Below are the reference conversions and FAQs from the previous version to ensure no information was lost.

Millimeters (mm)	Inches (Decimal)	Inches (Fraction)
1 mm	0.039	~ 5/128"
5 mm	0.197	~ 13/64"
10 mm	0.394	~ 25/64"
20 mm	0.787	~ 25/32"
25.4 mm	1.000	1"
50 mm	1.969	~ 1 31/32"
100 mm	3.937	~ 3 15/16"

FAQs

How many mm are in one inch? There are exactly 25.4 millimeters in one inch per the International Yard and Pound Agreement.

Is 10 mm half an inch? No. 10 mm is roughly 0.3937 inches, which is slightly more than 3/8" and just under 13/32".

How do you read mm to inches on a ruler? Compare the mm side to the inches side; 25.4 mm aligns perfectly with 1 inch.