Length and Area
mmtoin
Convert millimetres (mm) to inches (in).
Factor1 mm = 0.03937008 in
Converter
mm
Accepts numbers or expressions, e.g. 150 + 14.7
Result
in
Rendered to 6 significant figures.
Formula
Formula
in = mm × 0.03937008
Multiply any value in millimetres by 0.03937008 to obtain the value in inches.
Worked example
Convert 100 mm to in.
- 01Start with 100 mm.
- 02Multiply by the conversion factor: 100 × 0.03937008 = 3.93701 in.
Result100 mm = 3.93701 in
Conversion table
| mm | in |
|---|---|
| 1 | 0.03937 |
| 2 | 0.07874 |
| 5 | 0.19685 |
| 10 | 0.3937 |
| 20 | 0.7874 |
| 50 | 1.9685 |
| 100 | 3.937 |
| 200 | 7.874 |
| 500 | 19.685 |
| 1000 | 39.37 |
Reference values rounded to 5 significant figures for display.
FAQ
What is the conversion factor from mm to in?
1 mm equals 0.03937008 in. To convert, multiply the value in millimetres by 0.03937008.
How do I convert 1 mm to in?
1 mm = 0.0393701 in. For any value, multiply by 0.03937008.
How do I convert in back to mm?
Divide by the same factor — or equivalently, multiply by 25.4. So 1 in = 25.4 mm.
When would I need to convert millimetre to inch?
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 mm and in are defined by exact SI relationships, so the displayed factor is exact (any rounding shown is only for display).