About converting millimetres to inches
There are exactly 25.4 millimetres in an inch, so dividing by 25.4 is the whole conversion. Millimetres are the working unit for most engineering drawings outside the United States, which is why this conversion comes up constantly in fasteners, tooling and pipe sizes.
Watch for the difference between a converted size and a nominal one. A 10 mm bolt is 0.3937 inches, which is not the same as a 3/8 inch bolt at 0.375 inches - they are close enough to look interchangeable and are not.
Millimetre to Inch reference table
| Millimetre | Inch |
|---|---|
| 1 mm | 0.0393701 in |
| 2 mm | 0.0787402 in |
| 3 mm | 0.11811 in |
| 4 mm | 0.15748 in |
| 5 mm | 0.19685 in |
| 6 mm | 0.23622 in |
| 8 mm | 0.314961 in |
| 10 mm | 0.393701 in |
| 12 mm | 0.472441 in |
| 15 mm | 0.590551 in |
| 20 mm | 0.787402 in |
| 25 mm | 0.984252 in |
| 30 mm | 1.1811 in |
| 50 mm | 1.9685 in |
| 75 mm | 2.95276 in |
| 100 mm | 3.93701 in |
Frequently asked questions
- How many inches is 10 mm?
- 0.3937 inches, or a little under 13/32. It is very close to 3/8 inch (0.375) but not equal to it, which matters for anything threaded.
- What is 1 mm in inches as a fraction?
- About 1/25, or 0.03937 inches. Engineering drawings usually stay in decimal inches rather than fractions below about 1/16.
- Is anything I enter sent anywhere?
- No. The conversion runs inside your browser. Nothing you type is uploaded, stored or logged, and the page keeps working with the network disconnected.
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