Mm to inches
One mm equals 0.03937007874 in. Type any number and the answer appears as you type — the maths happens in your browser.
Result
The same value in every unit
| Unit | Value |
|---|
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Common values
| mm | inches |
|---|---|
| 1 mm | 0.039370079 in |
| 2 mm | 0.078740157 in |
| 3 mm | 0.11811024 in |
| 5 mm | 0.19685039 in |
| 10 mm | 0.39370079 in |
| 15 mm | 0.59055118 in |
| 20 mm | 0.78740157 in |
| 25 mm | 0.98425197 in |
| 50 mm | 1.9685039 in |
| 100 mm | 3.9370079 in |
| 500 mm | 19.685039 in |
| 1000 mm | 39.370079 in |
How to use
- Enter the number of mm in the field.
- The result in inches updates on every keystroke.
- Use the table below for the values people look up most often.
Formula and reverse conversion
The formula
To convert by hand: in = mm ÷ 25.4. Going back the other way, one in is 25.4 mm.
Where the odd number comes from
The factor is not a round number because the imperial units are defined through the metric ones by international agreement: an inch is exactly 25.4 mm and a pound is exactly 0.45359237 kg. Everything else follows from those definitions.
in = mm ÷ 25.4
Frequently asked questions
How many inches are in one mm?
One mm is 0.03937007874 in.
How do I convert mm to inches?
Multiply by the factor: in = mm ÷ 25.4.
Is the result exact?
The factors are the exact legal definitions, and up to ten significant digits are kept in the answer. Rounding happens only in the display.
How do I convert inches back to mm?
One in is 25.4 mm — or open the reverse page linked below.