Millimetres to Inches (mm to in)
1 mm = 0.03937008 in. Multiply millimetres by 0.03937008; the box below does it both ways.
5 mm = 0.19685 in · inches to millimetres page
How to convert millimetres to inches
- Take the value in millimetres.
- Multiply by 0.03937008 (because 1 mm = 0.03937008 in).
- Example: 5 mm × 0.03937008 = 0.19685 in.
- Going back: divide by 0.03937008, or multiply by 25.4.
Where this comes up
Divide millimetres by 25.4. Spanner, bolt and pipe sizes are where this bites: a 13 mm spanner is 0.512 in, which is why it almost fits a ½-inch bolt and rounds it. Plumbing in India mixes both systems (a ½-inch pipe is nominally 15 mm), so check the thread standard, not only the number.
| mm | in |
|---|---|
| 1 | 0.03937 |
| 2 | 0.07874 |
| 3 | 0.11811 |
| 5 | 0.19685 |
| 6 | 0.23622 |
| 8 | 0.31496 |
| 10 | 0.3937 |
| 12 | 0.47244 |
| 15 | 0.59055 |
| 20 | 0.7874 |
| 25 | 0.98425 |
| 25.4 | 1 |
| 50 | 1.9685 |
| 100 | 3.937 |
Questions people ask
How many inches are in 1 millimetre?
1 mm = 0.03937008 in. To convert, multiply the millimetre value by 0.03937008.
What is 12 mm in in?
12 mm is 0.47244 in.
How do I convert inches back to millimetres?
Divide by 0.03937008, or multiply by 25.4: 1 in = 25.4 mm.
More length conversions
Inches to Millimetres (in to mm) · m to ft · ft to m · cm to in · in to cm · cm to ft · ft to cm · ft to in · in to ft · cm to mm · mm to cm · all converters
Factors are the exact international definitions; last checked 2026-10-10.