How to convert inches to millimeters
mm = in × 25.4Multiply the value in inches by 25.4. To go the other way, multiply by 0.03937007874 (or divide by 25.4).
An inch is larger than a millimeter: one inch contains 25.4 millimeters.
Worked examples
- 1 inch1 in × 25.4 = 25.4 mm
- 5 inches5 in × 25.4 = 127 mm
- 10 inches10 in × 25.4 = 254 mm
- 20 inches20 in × 25.4 = 508 mm
- 100 inches100 in × 25.4 = 2,540 mm
Inches to millimeters conversion table
Values are calculated by the conversion engine and rounded to 8 significant figures.
| Inches (in) | Millimeters (mm) |
|---|---|
| 0.1 in | 2.54 mm |
| 0.25 in | 6.35 mm |
| 0.5 in | 12.7 mm |
| 1 in | 25.4 mm |
| 2 in | 50.8 mm |
| 3 in | 76.2 mm |
| 4 in | 101.6 mm |
| 5 in | 127 mm |
| 6 in | 152.4 mm |
| 7 in | 177.8 mm |
| 8 in | 203.2 mm |
| 9 in | 228.6 mm |
| 10 in | 254 mm |
| Inches (in) | Millimeters (mm) |
|---|---|
| 12 in | 304.8 mm |
| 15 in | 381 mm |
| 20 in | 508 mm |
| 25 in | 635 mm |
| 30 in | 762 mm |
| 40 in | 1,016 mm |
| 50 in | 1,270 mm |
| 75 in | 1,905 mm |
| 100 in | 2,540 mm |
| 250 in | 6,350 mm |
| 500 in | 12,700 mm |
| 1,000 in | 25,400 mm |
About the units
Inch (in)
A US customary and imperial unit defined as exactly 25.4 mm since 1959. Twelve inches make a foot. Screen sizes, tire diameters and lumber dimensions are usually given in inches. One inch equals 0.0254 meters (m).
Millimeter (mm)
One thousandth of a metre. Millimetres are the standard unit on engineering drawings, rulers and rainfall gauges; a credit card is about 0.76 mm thick. One millimeter equals 0.001 meters (m).
Frequently asked questions
How many millimeters are in one inch?
There are 25.4 millimeters in one inch, and this value is exact by definition.
How do I convert inches to millimeters?
Multiply the number of inches by 25.4. For example, 10 in × 25.4 = 254 mm.
How many inches are in one millimeter?
One millimeter equals 0.03937007874 inches. That is the reverse factor, 1 ÷ 25.4.
What is 10 inches in millimeters?
10 in = 254 mm.
Is this in to mm converter accurate?
Yes. Both units are defined exactly in terms of SI units, so the conversion factor is exact; results are shown to 12 significant figures by default and you can change precision in the converter. Calculations run in your browser using the same tested engine that generated this page.