Inches to Millimetres Converter
1 inch = 25.4 millimetres.
Enter a value
Result
1 inch =
25.4 mm
1 in × 25.4 = 25.4 mm
1 inch = 2.54 cm exactly · 1 mile = 1.609344 km exactly
The working
- 1. Convert 1 in to metres: 1 × 0.0254 = 0.0254.
- 2. Convert to mm: 0.0254 ÷ 0.001 = 25.4.
1 in in every unit
Handy reference lengths
- A4 sheet (long side)
- 29.7 cm
- Standard door height
- 2.03 m
- Football pitch
- 105 m
- Marathon
- 42.195 km
Conversion table
Inches to Millimetres
| Inches | Millimetres |
|---|---|
| 1 | 25.4 |
| 2 | 50.8 |
| 3 | 76.2 |
| 4 | 101.6 |
| 5 | 127 |
| 6 | 152.4 |
| 7 | 177.8 |
| 8 | 203.2 |
| 9 | 228.6 |
| 10 | 254 |
| 15 | 381 |
| 20 | 508 |
| 25 | 635 |
| 50 | 1,270 |
| 100 | 2,540 |
Millimetres to Inches
| Millimetres | Inches |
|---|---|
| 1 | 0.03937 |
| 2 | 0.07874 |
| 3 | 0.11811 |
| 4 | 0.15748 |
| 5 | 0.19685 |
| 6 | 0.23622 |
| 7 | 0.27559 |
| 8 | 0.31496 |
| 9 | 0.35433 |
| 10 | 0.3937 |
| 15 | 0.59055 |
| 20 | 0.7874 |
| 25 | 0.98425 |
| 50 | 1.9685 |
| 100 | 3.937 |
Formula and worked example
millimetres = inches × 25.4 (1 inch is exactly 2.54 cm).
Convert 0.5 inches to millimetres: 0.5 × 25.4 = 12.7 mm.
When you need this
Converting fractional inches such as 1/4 or 3/8 to millimetres is essential when replacing screws, sockets, pipe fittings or 3D-printing a part that was designed in imperial units.
Questions people ask
How many millimetres are in a inch?
One inch is 25.4 millimetres. 1 inch is exactly 2.54 cm.
How do I convert inches to millimetres?
Multiply the number of inches by 25.4.
What is 10 in in mm?
10 inches is 254 millimetres.
How do I convert millimetres back to inches?
Multiply by 0.039370079: one millimetre is 0.039370079 inches.
Related conversions
How we calculate this
We use the standard published formula or definition for this calculation, and we show the working so you can check it. Source: NIST Special Publication 811, Guide for the Use of the International System of Units.
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