About the mm to in calculation
One millimeter is exactly 0.03937 inches, so converting between them is a single multiplication. Enter any value above and the result updates as you type. The standard fine unit on engineering drawings and rainfall figures. Still standard for screen sizes, pipe diameters and tyre rims worldwide.
Formula
in = mm × 0.03937
1 mm = 0.03937 in
1 in = 25.4 mmWorked example
To convert 100 mm, multiply by 0.03937: 100 × 0.03937 = 3.937 in.
Frequently asked questions
How many inches are in a millimeter?
There are 0.03937 inches in one millimeter. To convert any amount, multiply the number of millimeters by 0.03937.
How do I convert inches back to millimeters?
Divide instead of multiplying, or equivalently multiply by 25.4. One inch is 25.4 millimeters.
Is this conversion exact?
Yes. Since the international agreement of 1959, the relationship between millimeters and inches is defined exactly rather than measured, so the only rounding here is in how many decimal places we show.
Where is each of these units used?
Millimeters: the standard fine unit on engineering drawings and rainfall figures. Inches: still standard for screen sizes, pipe diameters and tyre rims worldwide.
Sources
- NIST Special Publication 811 — Guide for the Use of the International System of Units