Inch Fraction to MM Converter
Enter a numerator and denominator to get the millimeter and decimal inch equivalent instantly.
/inches
Millimeters
9.525 mm
Decimal inches
0.375"
3 ÷ 8 = 0.375 in × 25.4 = 9.525 mm
The two-step conversion
Divide the numerator by the denominator to get decimal inches, then multiply by 25.4 to get millimeters. For 7/16": 7 ÷ 16 = 0.4375, then 0.4375 × 25.4 = 11.1125 mm.
The 25.4 mm-per-inch factor is exact, fixed by international agreement since 1959, so this conversion introduces no rounding error beyond whatever precision you carry the decimal to.
Common inch fractions in millimeters
| Fraction | Decimal (in) | Millimeters |
|---|---|---|
| 1/16" | 0.0625 | 1.5875 mm |
| 1/8" | 0.125 | 3.175 mm |
| 3/16" | 0.1875 | 4.7625 mm |
| 1/4" | 0.25 | 6.35 mm |
| 5/16" | 0.3125 | 7.9375 mm |
| 3/8" | 0.375 | 9.525 mm |
| 7/16" | 0.4375 | 11.1125 mm |
| 1/2" | 0.5 | 12.7 mm |
| 5/8" | 0.625 | 15.875 mm |
| 3/4" | 0.75 | 19.05 mm |
| 7/8" | 0.875 | 22.225 mm |
| 1" | 1.0 | 25.4 mm |
Full 1/64" reference and reverse lookup
For every inch fraction from 1/64" to 1" in one table, see the decimal equivalent chart. To go the other direction, from a millimeter measurement to the nearest inch fraction, use the MM to Fraction Inch Converter.
Frequently Asked Questions
Divide the fraction to get a decimal, then multiply by 25.4. For 3/8": 3 ÷ 8 = 0.375, then 0.375 × 25.4 = 9.525 mm.
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