How to convert inches to millimeters
To convert inches to millimeters, multiply by 25.4. Length conversions are used everywhere from construction drawings and travel distances to sewing patterns and science homework.
Inch to Millimeter conversion table
| Inch (in) | Millimeter (mm) |
|---|---|
| 0.1 in | 2.54 mm |
| 0.5 in | 12.7 mm |
| 1 in | 25.4 mm |
| 2 in | 50.8 mm |
| 3 in | 76.2 mm |
| 4 in | 101.6 mm |
| 5 in | 127 mm |
| 10 in | 254 mm |
| 20 in | 508 mm |
| 25 in | 635 mm |
| 50 in | 1,270 mm |
| 100 in | 2,540 mm |
| 500 in | 12,700 mm |
| 1,000 in | 25,400 mm |
About the units
Inch (in)
An inch is defined as exactly 2.54 centimeters. It is used in the US and UK for screen sizes, lumber and personal height.
Millimeter (mm)
A millimeter is one thousandth of a meter. It is the standard unit on engineering drawings, rulers and screw sizes.
How to use this converter
- Type the number of inches (in) in the input box.
- The result in millimeters appears instantly — no button needed.
- See the same value in every other length unit just below.
- Use “Swap units” to convert millimeters back to inches.
Tips for better results
- Double-check which system a unit belongs to (for example US vs UK gallons).
- Use the swap button to convert in the opposite direction instantly.
- Bookmark the conversions you use most — each pair has its own page.
Frequently asked questions
How many millimeters are in one inch?
One inch equals 25.4 millimeters. 25.4 is the exact factor used by this converter.
How do I convert inches to millimeters?
Multiply the value in inches by 25.4. To go the other way, multiply millimeters by 0.0393700787402.
What is 10 in in mm?
10 in = 254 mm. Also, 5 in = 127 mm and 100 in = 2,540 mm.
What is the difference between a inch and a millimeter?
An inch is defined as exactly 2.54 centimeters. It is used in the US and UK for screen sizes, lumber and personal height. A millimeter is one thousandth of a meter. It is the standard unit on engineering drawings, rulers and screw sizes.
Is this tool free and private?
Yes — the Inch to Millimeter is completely free with no sign-up, and it runs entirely in your browser, so the values you enter are never uploaded to our servers.
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