Inches to millimetres
Type a value in either box. 1 in = 25.4 mm.
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How to convert
To convert inches to millimetres, multiply by 25.4.
mm = in × 25.4
For example: 2 in × 25.4 = 50.8 mm.
An inch is defined as exactly 2.54 centimetres (since 1959).
In your head: Multiply by 25: 2 in ≈ 50 mm (exactly 50.8 mm), about 2% low.
When you’ll need it
Common fractions: 1/8 in is 3.175 mm, 1/4 in is 6.35 mm, 1/2 in is 12.7 mm and 3/4 in is 19.05 mm, which is why an imperial spanner rarely quite fits a metric nut.
Common values
| Inches (in) | Millimetres (mm) |
|---|---|
| 0.125 in | 3.175 mm |
| 0.25 in | 6.35 mm |
| 0.5 in | 12.7 mm |
| 0.75 in | 19.05 mm |
| 1 in | 25.4 mm |
| 1.5 in | 38.1 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 |
| 12 in | 304.8 mm |
Questions
- How many millimetres are in an inch?
- 1 inch is 25.4 millimetres.
- What is the formula to convert inches to millimetres?
- mm = in × 25.4. An inch is defined as exactly 2.54 centimetres (since 1959).
- What is 2 inches in millimetres?
- 2 inches is 50.8 millimetres.