Inches to MM Calculator
Enter a decimal inch value to get millimeters, centimeters, and meters instantly.
The formula
Millimeters = inches × 25.4. This factor is exact, not rounded, fixed by international agreement in 1959 when the major English-speaking countries standardized the inch against the metric meter.
Centimeters = inches × 2.54. Meters = inches × 0.0254. All three follow from the same 25.4 mm-per-inch constant, just scaled by a factor of 10 or 1000.
Common inch to mm values
| Inches | Millimeters |
|---|---|
| 1/4" (0.25) | 6.35 mm |
| 3/8" (0.375) | 9.525 mm |
| 1/2" (0.5) | 12.7 mm |
| 5/8" (0.625) | 15.875 mm |
| 3/4" (0.75) | 19.05 mm |
| 1" (1.0) | 25.4 mm |
| 2" (2.0) | 50.8 mm |
| 12" (12.0) | 304.8 mm |
Fractional inches convert the same way
A fractional inch converts to millimeters in two steps: divide the fraction to get a decimal, then multiply by 25.4. For 11/16": 11 ÷ 16 = 0.6875, then 0.6875 × 25.4 = 17.4625 mm. To go the other direction, from millimeters back to a fractional inch, use the MM to Inches Calculator or the MM to Fraction Inch Converter. For the full metric-to-imperial factor reference, see the metric conversion chart.
Frequently Asked Questions
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