THE EVERYDAY CONVERTER
Inches to mm converter
Millimetres = inches × 25.4. Use the swap button for the reverse conversion.
Length
Decimals and fractions welcome. Even 1 ½.
The same value, a few more ways.
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Smart precision shows up to 10 significant digits. Other settings round to the chosen decimal places. Scientific notation keeps very large and small results readable, including values that would otherwise round to zero. Calculations use the unrounded value. Feet-and-inches, stone-and-pounds and hours-and-minutes answers round the smaller unit to two decimal places.
Number formats: 1,000 means one thousand; 1,5 means one and a half. You can also use 1 000 or 1.000,5.
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Inches and millimetres: formulas
Millimetres = inches × 25.4
Inches = millimetres ÷ 25.4
Worked examples
A ⅜-inch measurement is 0.375 × 25.4 = 9.525 mm. A 50.8 mm measurement is 50.8 ÷ 25.4 = 2 inches.
Inches to millimetres table
Table results are rounded to six decimal places where needed. Use the calculator for other values or precision.
| Inches | Millimetres |
|---|---|
| 0 | 0 |
| 0.0625 | 1.5875 |
| 0.125 | 3.175 |
| 0.25 | 6.35 |
| 0.375 | 9.525 |
| 0.5 | 12.7 |
| 0.75 | 19.05 |
| 1 | 25.4 |
| 2 | 50.8 |
| 4 | 101.6 |
| 6 | 152.4 |
| 12 | 304.8 |
Which measurement does this use?
One inch is exactly 25.4 millimetres. A millimetre is one tenth of a centimetre. Keep enough decimal places for the job: rounding a converted measurement does not establish a manufacturing tolerance or guarantee that nominal tool sizes are interchangeable.
Can I convert fractional inch measurements?
Yes. Enter 3/8, ⅜ or 0.375 for the same result. If a specification gives a tolerance, preserve it separately; this calculator converts the number, not the allowed tolerance.
Reference: NIST conversion factors. Reviewed by Your Image 2 Canvas, 2 November 2026.
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