MM to Inches Converter
Millimeters into inches — hardware and workshop sizes, exactly.
Type in either field — the other updates instantly.
MM to Inches chart
| Millimeters | Inches |
|---|---|
| 1 mm | 0.04 in |
| 2 mm | 0.08 in |
| 3 mm | 0.12 in |
| 4 mm | 0.16 in |
| 5 mm | 0.2 in |
| 6 mm | 0.24 in |
| 8 mm | 0.31 in |
| 10 mm | 0.39 in |
| 12 mm | 0.47 in |
| 12.7 mm | 0.5 in |
| 15 mm | 0.59 in |
| 20 mm | 0.79 in |
| 25.4 mm | 1 in |
| 50 mm | 1.97 in |
| 100 mm | 3.94 in |
12.7 mm is exactly ½ in; 25.4 mm exactly 1 in.
How this is calculated
inches = mm ÷ 25.4 (exact — 1 in = 25.4 mm)
The caliper-and-catalog direction: a 10 mm socket is 0.3937 in, a 6 mm jewelry stone is 0.24 in, 3 mm plywood is about ⅛ in. Because workshops speak in fractions, the chart pairs each metric size with its nearest fractional inch and the exact decimal.
Exact by the inch’s definition (25.4 mm). The fraction column is the approximation — 3 mm is 0.1181 in, "close to 1/8" (0.125 in) with 5.5% slack — the page shows both so the tolerance decision is yours.
Millimetres to inches is the workshop conversion — engineering drawings, fastener sizes, sheet thicknesses and printing dimensions. Because one inch is exactly 25.4 mm, this conversion is exact in both directions, which is why the millimetre has become the standard unit on technical drawings even in countries that otherwise use inches.
The practical difficulty is that a decimal inch has to be read on a tool graduated in fractions. 10 mm is 0.3937 inches, which is a shade under 25/64 — a fraction most tapes do not show. Where a job needs a fractional inch, work to the nearest sixteenth or thirty-second and note the residual error rather than pretending the decimal was achievable.
Frequently asked questions
How many inches is 10 mm?
0.3937 in — just under 13/32. In socket-set terms, 10 mm sits between 3/8 (9.53 mm) and 7/16 (11.11 mm), which is why metric and SAE sets both exist.
What is 3 mm in fractions of an inch?
0.1181 in ≈ 1/8 in (which is 3.175 mm). The 0.175 mm gap matters in machining and vanishes in craft work — the chart shows exact decimals so you can judge.
Why 25.4 exactly?
The 1959 international agreement defined the inch as exactly 25.4 mm, ending centuries of slightly different national inches. Every conversion on this page inherits that exactness.
How do I convert drill bit sizes?
Metric bits are labeled in mm; US twist bits use fractions, letters, and numbers. Convert the mm size here, then pick the nearest larger fraction for clearance holes or smaller for pilot holes.