Inches to mm
Convert inches to millimeters instantly.
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Formula
1 inch = 25.4 mm
Unit Relationship
One inch equals exactly 25.4 millimeters.
Worked Example
Multiply inches by 25.4. For 10 inches: 10 × 25.4 = 254 millimeters.
Unit Definitions
Inches: an imperial and US customary unit equal to 1/12 of a foot.
mm: a metric unit equal to one-thousandth of a meter.
Practical Uses
- Converting mechanical and construction dimensions to metric units.
- Converting product dimensions and material thicknesses from inches to millimeters.
- Comparing imperial fastener or component dimensions with metric specifications.
Precision and Rounding
The inch is defined exactly as 25.4 millimeters, so the conversion factor itself is exact.
Important Notes
- Decimal inches and fractional inches should first be represented as a numeric inch value.
- Keep extra decimal places when checking tolerances or component dimensions.
Quick Reference
| Inches | mm |
|---|
| 1 | 25.4 |
| 5 | 127 |
| 10 | 254 |
| 100 | 2540 |
Frequently Asked Questions
How many millimeters are in one inch?
One inch equals exactly 25.4 millimeters.
How do I convert inches to millimeters?
Multiply inches by 25.4.
Is 25.4 millimeters per inch exact?
Yes. The international inch is defined as exactly 25.4 millimeters.
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