How many millimeter are in one inch?
One inch is 25.4 mm.
Inch to Millimeter
Type a value to convert it from inch to millimeter. One in equals 25.4 mm.
Result
Inch and Millimeter, 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: the imperial 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.
| Inch | Millimeter |
|---|---|
| 1 | 25.4 |
| 5 | 127 |
| 10 | 254 |
| 20 | 508 |
| 50 | 1270 |
| 100 | 2540 |
Frequently asked questions
How do I convert millimeter back to inch?
One millimeter is 0.03937 in. The tool above converts in both directions.
Other tools
Ethanol or Gasoline
Which fuel pays off at today’s prices, for your car.
Weight Converter
Kilograms to pounds, grams to ounces, and back again.
Temperature Converter
Celsius to Fahrenheit and Kelvin, with the offset done right.
Area Converter
Square meters, square feet, hectares and acres.
Volume Converter
Liters to gallons, milliliters to fluid ounces.
Fraction Calculator
Add, subtract, multiply and divide fractions — exactly, never rounded.