Inches to MM Converter
Inches into millimeters — decimals in, exact metric out.
Type in either field — the other updates instantly.
Inches to MM chart
| Inches | Millimeters |
|---|---|
| 0.0625 in | 1.59 mm |
| 0.125 in | 3.18 mm |
| 0.1875 in | 4.76 mm |
| 0.25 in | 6.35 mm |
| 0.375 in | 9.52 mm |
| 0.5 in | 12.7 mm |
| 0.625 in | 15.88 mm |
| 0.75 in | 19.05 mm |
| 1 in | 25.4 mm |
| 1.5 in | 38.1 mm |
| 2 in | 50.8 mm |
| 4 in | 101.6 mm |
| 12 in | 304.8 mm |
The rows are the workshop fractions: 1/16, 1/8, 3/16, 1/4, 3/8, 1/2, 5/8, 3/4.
How this is calculated
mm = inches × 25.4 (exact)
The drawing-to-metric direction: 0.375 in (3/8) is 9.525 mm, 0.5 in is 12.7 mm, a 1.75 in pipe is 44.45 mm. Enter fractions as decimals (1/16 = 0.0625, 1/8 = 0.125, 3/16 = 0.1875) and the ×25.4 multiply is exact every time.
Exact by definition — and conveniently reversible in your head: the common fractions land on clean metric numbers (1/2 in = 12.7 mm, 1/4 = 6.35, 1/8 = 3.175), a byproduct of the 25.4 definition.
Inches to millimetres is how imperial drawings become machinable parts. Drilling, tapping, sheet metal and 3D printing are all specified in millimetres in most of the world, so an American plan has to be converted before anything is cut — and because one inch is exactly 25.4 mm, the conversion introduces no error of its own.
Fractional inches convert to awkward millimetre values, which is the source of most fit problems: 1/4" is 6.35 mm, so a 6 mm hole is too small and a 6.5 mm hole is loose. That is why imperial fasteners need imperial drill sizes rather than the nearest metric one, and why mixing the two systems in a single assembly causes trouble long after the arithmetic was done correctly.
Frequently asked questions
What is 3/8 inch in mm?
9.525 mm exactly (0.375 × 25.4). Rounded 9.5 mm is fine for woodwork; machinists keep the last digit.
How do I enter fractions?
As decimals: divide top by bottom. 5/16 = 0.3125 → 7.9375 mm. The chart above covers the standard set so most lookups need no division at all.
What is 1 inch in mm — exactly?
25.4 mm, exact by international definition since 1959. Not 25, not 25.5 — the difference is a broken fit in anything precision.
Are TV inches converted the same way?
Yes — a 65-inch screen has a 1,651 mm diagonal. Width and height then depend on the 16:9 shape: roughly 1,439 × 809 mm for that 65.