Inches to mm Converter

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Convert inches to millimeters with the exact international factor 1 inch = 25.4 mm. Common use cases: drill bit and tap sizing, photographic film dimensions, picture-frame matting, and buying US tooling for a metric workshop. Two-way live conversion runs in your browser with no upload or logging.

Inch (in)
Millimeter (mm)

Inch (in) → Millimeter (mm)

Quick reference table

Inch (in)Millimeter (mm)
1 inch25.4 mm
2 inch50.8 mm
5 inch127 mm
10 inch254 mm
25 inch635 mm
50 inch1270 mm
100 inch2540 mm

Glossary

Inch (in)

An inch is the base small unit of the imperial and US customary systems, defined as exactly 25.4 mm since 1959. It appears on screen sizes, tire diameters, pipe fittings, lumber dimensions and DIY tape measures. Twelve inches make one foot; thirty-six make one yard.

Millimeter (mm)

A millimeter is one thousandth of a meter (1 mm = 0.1 cm = 0.03937 inch). It is the default fine-resolution unit on rulers, mechanical drawings, electronics PCBs and rainfall gauges. Ten millimeters make a centimeter; one inch contains exactly 25.4 millimeters by international agreement since 1959.

Metric system (SI)

The metric system is a decimal system of measurement built around the meter for length, the kilogram for mass and the second for time, with multiples and submultiples expressed as powers of ten (millimeter, centimeter, kilometer). Adopted in France in 1799 and codified internationally as the International System of Units (SI) in 1960, it is now the official measurement system in nearly every country and the standard in science and engineering worldwide.

Imperial / US Customary system

The imperial system is the historical English system of weights and measures whose length units are the inch, foot, yard and mile (12 in = 1 ft, 3 ft = 1 yd, 1,760 yd = 1 mi). Codified by the British Weights and Measures Act of 1824 and aligned with US Customary by the international yard-and-pound agreement of 1959 (1 inch = 25.4 mm exactly), it is still used in the United States, the United Kingdom and a handful of other countries for everyday distances.

Related tools

Millimeters to Inches
Convert millimeters to inches — 1 mm = 0.03937 in (1 in = 25.4 mm)
Inches to Centimeters
Convert inches to centimeters — 1 inch = 2.54 cm exactly
Inches to Feet
Convert inches to feet — 12 in = 1 ft (1 in = 0.0833 ft)
Length Converter
Convert length units between metric and imperial — mm, cm, m, km, inches, feet, yards, miles