Inches to Millimetres
Convert inches (in) to millimetres (mm) instantly — with formula and reference table.
in
mm
Quick answer: 1 in = 25.4 mm. To convert inches to millimetres, multiply by in × 25.4.
Converting inches to millimetres
This converter changes a value in inches (in) into millimetres (mm). One inche equals 25.4 mm. One inch equals exactly 25.4 millimetres, so inches-to-millimetres is a direct multiplication by 25.4. The conversion runs entirely in your browser — enter a value and the result updates instantly, in either direction.
Formula
mm = in × 25.4
Example
Convert 10 in to mm: 10 × 25.4 = 254 mm.
Inches to Millimetres conversion table
| Inches (in) | Millimetres (mm) |
|---|---|
| 1 in | 25.4 mm |
| 2 in | 50.8 mm |
| 3 in | 76.2 mm |
| 5 in | 127 mm |
| 10 in | 254 mm |
| 20 in | 508 mm |
| 25 in | 635 mm |
| 50 in | 1270 mm |
| 100 in | 2540 mm |
How to use this converter
- Enter a value in the inches (in) field.
- Read the converted value in millimetres (mm) below.
- Type into the mm field instead to convert in reverse, or use the swap button.
Frequently asked questions
How many millimetres are in an inch?
1 inch equals exactly 25.4 millimetres.
How do I convert 6 inches to mm?
6 times 25.4 = 152.4 mm.
Why convert inches to mm?
Engineering and manufacturing drawings frequently use millimetres, so inch dimensions are converted for precision machining.