Inches to Millimeters
Convert in to mm quickly with this free online calculator. The page explains the conversion rule, gives practical examples and provides a quick reference table.
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CONVERTED RESULT—
Decimal places
CONVERSION RULE
1 inch equals 25.4 millimeters.
How to use the Inches to Millimeters
- Enter the number you want to convert.
- Confirm the source unit shown beside the input.
- Choose decimal precision if you need more or less detail.
- Read the converted result.
- Copy the result when you need to use it elsewhere.
How the conversion works
1 inch equals 25.4 millimeters.
For a simple fixed-factor conversion, the calculator multiplies the entered value by the stated factor. Temperature scales and certain specialized tools use their specific mathematical relationship instead.
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Common in to mm conversions
| in | mm |
|---|---|
| 1 in | 25.4 mm |
| 2 in | 50.8 mm |
| 5 in | 127 mm |
| 10 in | 254 mm |
| 20 in | 508 mm |
| 50 in | 1,270 mm |
Example
For example, entering 1 in gives approximately 25.4 mm using the rule above. Change the input to test your own value.
Frequently asked questions
The Inches to Millimeters converts a value from in to mm using the conversion relationship described on this page.
Enter your value, review the source and destination units, choose the decimal precision and read or copy the result.
1 inch equals 25.4 millimeters.
Use enough precision for your purpose. Everyday estimates usually need fewer decimal places; technical work may require more.
It can be a useful reference calculation, but safety-critical, regulated, contractual or specialized work should be verified against the applicable authoritative standard.
Accuracy note: This calculator is a practical reference. For regulated, safety-critical or specialized work, verify the result against the applicable standard.
Page reviewed: August 24, 2026.