mm to Inches Converter

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Convert millimeters to inches at the exact rate of 1 mm = 0.03937 inch, the inverse of the 1959 definition 1 inch = 25.4 mm. Engineers use this for mechanical drawings that mix metric and imperial fasteners, woodworkers for board thickness, jewellers for stone sizes. All math runs in your browser — your numbers stay on your device.

Millimeter (mm)
Inch (in)

Millimeter (mm) → Inch (in)

Quick reference table

Millimeter (mm)Inch (in)
1 mm0.0394 inch
2 mm0.0787 inch
5 mm0.1969 inch
10 mm0.3937 inch
25 mm0.9843 inch
50 mm1.9685 inch
100 mm3.937 inch

Glossary

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.

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.

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.

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