Convert Inches to Millimeters
Convert Inches to Millimeters instantly with the exact formula (1 in = 25.4 mm), a quick table and the reverse conversion.
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How to use Inches to Millimeters Converter
- 1
Open Inches to Millimeters Converter on this page. It loads right in your browser.
- 2
Add your file, text or values and adjust the settings.
- 3
Copy the result or download it. Nothing is uploaded or stored.
About this tool
This converter turns Inches into Millimeters as you type. One inch equals 25.4 mm, so the result is exact, not rounded guesswork. It is handy for heights, screen sizes, furniture, clothing, DIY projects and maps.
How to convert Inches to Millimeters
Multiply the value in Inches by 25.4. To convert Inches to Millimeters, use the formula below.
mm = in × 25.4
Worked example
12 in × 25.4 = 304.8 mm
Quick mental estimate
For a rough figure in your head, multiply by about 25: 12 in ≈ 300 mm. Use the converter when you need the exact value.
Inches to Millimeters table
| Inches (in) | Millimeters (mm) |
|---|---|
| 1 | 25.4 |
| 2 | 50.8 |
| 5 | 127 |
| 10 | 254 |
| 12 | 304.8 |
| 15 | 381 |
| 20 | 508 |
| 25 | 635 |
| 30 | 762 |
| 50 | 1270 |
| 75 | 1905 |
| 100 | 2540 |
Quick reference
- 2 in = 50.8 mm
- 10 in = 254 mm
- 15 in = 381 mm
- 25 in = 635 mm
- 50 in = 1270 mm
- 100 in = 2540 mm
Where Inches and Millimeters are used
The metric system (millimeters, centimeters, meters, kilometers) is used almost everywhere, while the United States, and partly the UK, still use inches, feet, yards and miles for everyday lengths. Product listings, construction plans and sports often mix both, which is why conversions are needed so often.
Tips
- Use the swap button to convert Millimeters back to Inches.
- Choose 0 to 6 decimals; the full-precision value is used internally.
- The side panel also shows the value in every other unit of the same type.
Why use this converter
It is free, needs no sign-up and runs entirely in your browser, so it keeps working even offline once the page is loaded. Need the opposite? Use the Millimeters to Inches converter or the full unit converter.
Features
- Instant Inches to Millimeters conversion as you type
- Exact factor: 1 in = 25.4 mm
- Quick conversion table of common values
- Swap button for Millimeters to Inches
- Choose 0 to 6 decimal places
- Works offline in your browser
Frequently asked questions
How many Millimeters are in one inch?
One inch equals 25.4 mm.
How do I convert Inches to Millimeters?
Multiply the number of Inches by 25.4. For example, 12 in = 304.8 mm.
What is 25 in in Millimeters?
25 in equals 635 mm.
Is the conversion exact?
Yes. The tool uses the internationally defined conversion factor and only rounds the displayed result to the decimals you choose.