Convert inches to millimetres
Enter a value in inches (in) to get millimetres (mm). One inch is 25.4 millimetres; one millimetre is 0.03937 inches.
How to use the Inch to millimetre
- Type the number of inches.
- Click Convert.
- Read the result in millimetres, plus the same value in every other length unit.
in to mm formula
millimetres = inches × 25.4. To go the other way, inches = millimetres × 0.03937 (see millimetres to inches).
Worked example
12 in × 25.4 = 304.8 mm.
Inches to millimetres conversion table
| Inches | Millimetres |
|---|---|
| 0.1 in | 2.54 mm |
| 0.5 in | 12.7 mm |
| 1 in | 25.4 mm |
| 2 in | 50.8 mm |
| 3 in | 76.2 mm |
| 5 in | 127 mm |
| 10 in | 254 mm |
| 20 in | 508 mm |
| 25 in | 635 mm |
| 50 in | 1,270 mm |
| 100 in | 2,540 mm |
| 250 in | 6,350 mm |
| 500 in | 12,700 mm |
| 1,000 in | 25,400 mm |
About the inch
Exactly 25.4 mm since the 1959 international yard and pound agreement. Screens, tyres and paper in the USA and UK are still sized in inches.
About the millimetre
One thousandth of a metre. Used for engineering drawings, paper sizes and small measurements; a credit card is about 0.8 mm thick.
Related conversions
millimetres to inches · inches to centimetres · inches to feet · any unit.
Frequently asked questions
How many millimetres in a inch?
25.4 millimetres.
How many inches in a millimetre?
0.03937 inches.
Is the factor exact?
The factor 25.4 is derived from the units' exact definitions; only the display is rounded.
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Last updated 2026-09-23.