Millimeters to Inches (mm to in) Converter
1 millimeter equals 0.03937008 inches — multiply the number of millimeters by 0.03937008 to convert to inches. This is the exact factor because one inch is defined as precisely 25.4 millimeters, and 1 ÷ 25.4 = 0.03937008. The relationship is fixed, so the answer is always precise.
The formula
To convert millimeters to inches, multiply by the exact factor:
inches = millimeters × 0.03937008
For example, 30 mm × 0.03937008 = 1.181 in. To go the other way, multiply inches by 25.4 to get millimeters.
Conversion table
| Millimeters (mm) | Inches (in) |
|---|---|
| 1 | 0.03937008 |
| 2 | 0.07874016 |
| 5 | 0.19685039 |
| 10 | 0.39370079 |
| 25 | 0.98425197 |
| 50 | 1.96850394 |
| 100 | 3.93700787 |
| 250 | 9.84251969 |
| 500 | 19.68503937 |
| 1000 | 39.37007874 |
How to convert online
- Type the number of millimeters into the first box.
- Read the inch value instantly in the second box.
- Or enter an inch value to convert back to millimeters — it works both ways.
Use the Millimeter to Inch Converter — free and instant in your browser.
Where this conversion is used
Millimeter-to-inch conversion is everyday work in engineering drawings, 3D printing, woodworking and sewing, where metric CAD dimensions meet imperial rulers. It also appears in phone and screen specs, camera lens sizes, jewelry and any project mixing European parts with US measurements.
Worked example
Suppose a datasheet lists a bolt as 45 mm long and you need the size in inches for a US supplier. Apply the formula: 45 × 0.03937008 = 1.7716535 in, which is just over 1¾ inches. If you instead measured a shelf at 600 mm, then 600 × 0.03937008 = 23.6220472 in, or about 23⅝ inches. Working the other direction, a ½-inch (0.5 in) fastener is 0.5 × 25.4 = 12.7 mm. Because the 0.03937008 factor is exact, you can trust these results to the last decimal without accumulating rounding error across a parts list.
FAQ
How many inches are in a millimeter?
One millimeter equals 0.03937008 inches. Multiply millimeters by 0.03937008 — for example, 10 mm = 0.39370079 in.
How do I convert inches back to millimeters?
Divide by 0.03937008, or simply multiply inches by 25.4. So 2 in = 50.8 mm.
Is the conversion exact?
Yes. One inch is defined as exactly 25.4 mm, so 1 mm = 0.03937008 in is exact to eight decimal places; the tool applies the full-precision factor automatically.
What is 100 mm in inches?
100 mm equals 3.93700787 inches, just under 4 inches. Multiply by the same 0.03937008 factor for any value: 250 mm is 9.84251969 in and 500 mm is 19.68503937 in.
Related converters
- Inch to Millimeter Converter
- Millimeter to Centimeter Converter
- Millimeter to Meter Converter
- Millimeter to Foot Converter
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