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Inches to MM converter
Enter a number, fraction, power, π, or arithmetic expression.1 in = 25.4 mm millimeters = inches × 25.4
Ready for local conversionInches to MM formula
millimeters = inches × 25.4
1 inch = exactly 25.4 millimeters
The international yard and pound agreement fixed the inch at exactly 25.4 millimeters, eliminating older regional differences for ordinary use.
How to convert Inches to Millimeters
Multiply the inch value by 25.4. Mixed numbers and fractions can be entered as expressions, so 3 3/8 inches can be converted without first reaching for another calculator.
Example calculation
An 8.5-inch sheet width is 215.9 mm: 8.5 × 25.4 = 215.9.
8.5 in = 215.9 mm
When this conversion is useful
Use this page when an inch-based drawing must be entered into metric CAD, when comparing bolt diameters, or when checking material thickness against a millimeter specification.
Common Inches to Millimeters conversions
| Inches (in) | Millimeters (mm) |
|---|---|
| 1 | 25.4 |
| 2 | 50.8 |
| 3.375 | 85.725 |
| 6 | 152.4 |
| 8.5 | 215.9 |
| 12 | 304.8 |
Inches to MM FAQ
One inch contains exactly 25.4 millimeters.
Half an inch is exactly 12.7 millimeters because 0.5 × 25.4 = 12.7.
Yes. Enter values such as 1/8, 3/4, or 2 5/16. The expression is evaluated first and then sent through the same conversion engine.