Millimeters to Inches Converter
Enter a value to instantly convert between length units.
1 Millimeter = 0.0394 Inch
Key Formulas
Centimeter → Inch
in = cm × 0.393701Kilometer → Mile
mi = km × 0.621371Foot → Meter
m = ft × 0.3048Inch → Centimeter
cm = in × 2.54Formula
in = mm × 0.03937008The inch is defined as exactly 25.4 mm, making millimeters the precise metric counterpart for fine measurements. The conversion is exact — no approximation involved. This matters in manufacturing, CNC machining, 3D printing, and imported hardware where technical drawings switch between metric and imperial specs.
Source: NIST SP 811, Table B.8
Frequently Asked Questions
Real-World Examples
25.4 mm is exactly 1 inch — the international definition since 1959
25.4 mm = 1 in
A 6 mm drill bit is roughly 15/64 inch — common when matching metric bits to imperial pilot hole specs
6 mm = 0.2362 in
10 mm socket = about 3/8 inch — close but not interchangeable with a 3/8 in (9.525 mm) tool
10 mm = 0.3937 in
A 200 mm build plate on a 3D printer is just under 8 inches — relevant when sourcing replacement glass or PEI sheets in the US
200 mm = 7.874 in