Inches to Millimetres Converter
This free length converter changes inches (in) into millimetres (mm) and back again. Millimetres are the standard unit in engineering drawings, machining and manufacturing, so this is handy when working from imperial dimensions.
How it works
The inch is defined as exactly 25.4 millimetres, so the conversion is a single exact multiplication:
millimetres = inches × 25.4
The converter is bidirectional: type in the inches field to multiply by 25.4, or type in the millimetres field to divide by 25.4 and get inches. Both update in real time.
Example
To convert 10 inches: 10 × 25.4 = 254 mm. Going the other way, 127 mm ÷ 25.4 = 5 in.
| Inches (in) | Millimetres (mm) |
|---|---|
| 1 in | 25.4 mm |
| 5 in | 127 mm |
| 10 in | 254 mm |
| 100 in | 2540 mm |
All calculations run entirely in your browser with no data sent to any server.