Inches to Millimetres
Convert inches to millimetres (in to mm). 1 in = 25.4 mm. Use the calculator, formula and conversion table.
How to convert inches to millimetres
Multiply the amount in inches by 25.4 to get millimetres. The displayed factor and results are rounded to 12 significant digits.
mm = in × 25.4Worked example
1 in = 25.4 mm. Change the amount in the calculator above to use your own value.
Units and assumptions
Uses international metric and imperial definitions. One inch is exactly 0.0254 metres; one foot is 12 inches. These are lengths, rather than areas or volumes.
Calculator results use floating-point arithmetic and are rounded for display. The reference table below uses up to 12 significant digits.
Inches to Millimetres table
| Inches (in) | Millimetres (mm) |
|---|---|
| 0 | 0 |
| 1 | 25.4 |
| 5 | 127 |
| 10 | 254 |
| 25 | 635 |
| 100 | 2,540 |
| 1,000 | 25,400 |
About this conversion
What is the formula for inches to millimetres?
mm = in × 25.4. Multiply the amount in inches by 25.4 to get millimetres. The displayed factor and results are rounded to 12 significant digits.
How do I convert back to inches?
Use the millimetres to inches calculator to reverse this conversion. You can also use Swap units in the calculator above.
Can I use a different pair of units?
Choose another unit in the calculator, or open the length converter to browse all supported pairs.