How many inches are in a millimeter?

1 mm = 0.03937 in. To convert any amount, multiply by 0.03937.

How do you convert millimeters to inches?

Multiply the number of millimeters by 0.03937 to get inches. The formula is shown in the "How it's calculated" section above.

Where does the conversion factor come from?

It's a published international standard. Most are defined exactly by international agreement (e.g. 1 inch = 25.4 mm exactly, 1 lb = 0.45359237 kg exactly). Source citations are listed under the formula above.

Unit converter — Length

Millimeters to inches converter

Convert millimeters (mm) to inches (in). Source-cited conversion factor, exact to the displayed precision.

Results are mathematically exact for the displayed precision. How we calculate.

How it's calculated

Convert millimeters to inches— the formula

Millimeters convert to inches by multiplying by the published conversion factor. The factor below is exact to the precision shown, sourced from the citation under the formula.

in = mm × 0.03937

mm = in × 25.4

SI base unit (BIPM). US customary lengths from the 1959 international yard agreement: 1 yd = 0.9144 m exactly, 1 in = 25.4 mm exactly, 1 mi = 1609.344 m exactly.

Questions

Frequently asked questions

How many inches are in a millimeter?
1 mm = 0.03937 in. To convert any amount, multiply by 0.03937.
How do you convert millimeters to inches?
Multiply the number of millimeters by 0.03937 to get inches. The formula is shown in the "How it's calculated" section above.
Where does the conversion factor come from?
It's a published international standard. Most are defined exactly by international agreement (e.g. 1 inch = 25.4 mm exactly, 1 lb = 0.45359237 kg exactly). Source citations are listed under the formula above.