Your result will appear here
Fill in the fields and press Calculate.
Millimetres give fine, precise measurements; inches are the imperial equivalent used in much of the US and UK trade. For screws, timber, screens and engineering drawings you often need to switch between them — this converter does it exactly.
How is it calculated?
The conversion factor
1 inch = 25.4 millimetres exactly.
| To convert | Do this |
|---|---|
| mm → inches | divide by 25.4 |
| inches → mm | multiply by 25.4 |
Common values
| Millimetres | Inches |
|---|---|
| 1 mm | 0.039 in |
| 10 mm | 0.394 in |
| 25.4 mm | 1.000 in |
| 100 mm | 3.937 in |
Worked example
A 6 mm drill bit is 6 ÷ 25.4 = 0.236 inches, close to the ¼-inch (0.25 in) size. A ½-inch pipe is 0.5 × 25.4 = 12.7 mm.
FAQ
How many inches is 1 mm?+
One millimetre is 0.03937 inches — about a twenty-fifth of an inch. Divide millimetres by 25.4 to get inches.
How do I convert mm to inches?+
Divide the millimetre value by 25.4, since an inch is defined as exactly 25.4 mm. For example, 50 mm ÷ 25.4 = 1.969 inches.
How many mm in an inch?+
Exactly 25.4 millimetres. This has been the international definition of the inch since 1959, so the conversion is precise.
How do I convert inches to mm?+
Multiply the inch value by 25.4. A ¾-inch bolt is 0.75 × 25.4 = 19.05 mm.
What is 100 mm in inches?+
100 mm is 3.937 inches, just under 4 inches (which would be 101.6 mm).