Millimeters to Inches Converter
Two-way converter: change millimeters to inches or inches to millimeters in one step.
Type a value in either field for an instant conversion
About converting millimeters and inches
The millimeter is a small metric unit of length, while the inch is used in imperial standards in the US and UK. One inch equals exactly 25.4 millimeters, so this conversion shows up when working with threads, pipes, fasteners, and imperial drawings.
To convert millimeters to inches, divide the value by 25.4. To go back from inches to millimeters, multiply the number of inches by 25.4. This converter handles both directions automatically.
Every calculation runs locally in your browser and updates instantly — nothing is uploaded, and the result appears the moment you type.
Why use this converter
Works both ways
Convert mm to inches or inches to mm by typing in either field.
Exact accuracy
Uses the official factor of 1 inch = 25.4 mm with no rounding.
No install
Runs in any browser on phone or desktop, with no sign-up required.
Frequently asked questions
How many millimeters are in one inch?
One inch equals exactly 25.4 millimeters. This is the internationally agreed value.
How many inches are in one millimeter?
One millimeter equals about 0.03937 inches. To convert mm to inches, divide the value by 25.4.
How do I convert inches to mm?
Multiply the number of inches by 25.4. For example, 2 inches = 50.8 mm.
Why convert millimeters to inches?
Imperial sizes appear in plumbing threads, pipe diameters, fasteners, and technical documentation from the US and UK.
Is the converter accurate?
Yes, it uses the exact factor of 25.4 mm per inch, so the result matches the standard.