Length and Area
intomm
Convert inches (in) to millimetres (mm).
Factor1 in = 25.4 mm
Converter
in
Accepts numbers or expressions, e.g. 150 + 14.7
Result
mm
Rendered to 6 significant figures.
Formula
Formula
mm = in × 25.4
Multiply any value in inches by 25.4 to obtain the value in millimetres.
Worked example
Convert 6 in to mm.
- 01Start with 6 in.
- 02Multiply by the conversion factor: 6 × 25.4 = 152.4 mm.
Result6 in = 152.4 mm
Conversion table
| in | mm |
|---|---|
| 1 | 25.4 |
| 2 | 50.8 |
| 5 | 127 |
| 10 | 254 |
| 20 | 508 |
| 50 | 1270 |
| 100 | 2540 |
| 200 | 5080 |
| 500 | 12700 |
| 1000 | 25400 |
Reference values rounded to 5 significant figures for display.
FAQ
What is the conversion factor from in to mm?
1 in equals 25.4 mm. To convert, multiply the value in inches by 25.4.
How do I convert 1 in to mm?
1 in = 25.4 mm. For any value, multiply by 25.4.
How do I convert mm back to in?
Divide by the same factor — or equivalently, multiply by 0.03937008. So 1 mm = 0.0393701 in.
When would I need to convert inch to millimetre?
Length conversions appear in piping, layout, and mechanical drawings — particularly when reconciling imperial fittings or instrument lengths with metric plant drawings.
Is the conversion exact?
Yes. Both in and mm are defined by exact SI relationships, so the displayed factor is exact (any rounding shown is only for display).