How many millimeters are in one inch?
One inch is 25.4 mm.
Inches to Millimeters
Type a value to convert it from inches to millimeters. One in equals 25.4 mm.
Result
Inches and millimeters, side by side
One inch is 25.4 mm. In the other direction, one millimeter is 0.03937 in.
The factor is exact rather than rounded: imperial and US units have been defined from the metric ones since 1959, so the conversion introduces no error of its own. What you see below is arithmetic, not an approximation.
The inch has been exactly 2.54 centimeters since the international yard and pound agreement of 1959. It survives worldwide in screen sizes, which measure the diagonal, in wheel rims and in pipe fittings, and in the United States for everyday lengths.
The millimeter is one thousandth of a meter, the unit of technical drawings and machine shops. Rainfall is measured in it, it is the smallest division on most rulers, and a credit card is about 0.76 mm thick.
| Inch | Millimeter |
|---|---|
| 1 | 25.4 |
| 5 | 127 |
| 10 | 254 |
| 20 | 508 |
| 50 | 1,270 |
| 100 | 2,540 |
Frequently asked questions
How do I convert millimeters back to inches?
One millimeter is 0.03937 in. The tool above converts in both directions.
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