Inches to millimetres converter
Millimetres (mm)
1 inch = 25.4 millimetres
How to convert inches to millimetres
mm = in × 25.4
Multiply the number of inches by 25.4 to get millimetres. Going the other way, divide by 25.4 (or multiply by 0.0393700787402).
One inch is exactly defined as 25.4 millimetres (to 12 significant figures), and one millimetre is 0.0393700787402 inches.
Worked examples
- Convert 5 inches: 5 × 25.4 = 127 127 millimetres.
- Convert 12.5 inches: 12.5 × 25.4 = 317.5 317.5 millimetres.
- Convert 250 inches: 250 × 25.4 = 6,350 6,350 millimetres.
Quick-reference table
| in | mm |
|---|---|
| 1 | 25.4 |
| 2 | 50.8 |
| 3 | 76.2 |
| 5 | 127 |
| 10 | 254 |
| 15 | 381 |
| 20 | 508 |
| 25 | 635 |
| 50 | 1,270 |
| 75 | 1,905 |
| 100 | 2,540 |
| 1,000 | 25,400 |
| mm | in |
|---|---|
| 1 | 0.03937007874 |
| 2 | 0.07874015748 |
| 3 | 0.1181102362 |
| 5 | 0.1968503937 |
| 10 | 0.3937007874 |
| 15 | 0.5905511811 |
| 20 | 0.7874015748 |
| 25 | 0.9842519685 |
| 50 | 1.968503937 |
| 75 | 2.952755906 |
| 100 | 3.937007874 |
| 1,000 | 39.37007874 |
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Frequently asked questions
How many millimetres are in 1 inch?
1 inch equals 25.4 millimetres.
What is the formula to convert inches to millimetres?
Use mm = in × 25.4. Multiply the number of inches by 25.4 to get millimetres. Going the other way, divide by 25.4 (or multiply by 0.0393700787402).
What is 100 inches in millimetres?
100 inches is 2,540 millimetres.