Unit Converters

Mm to inches converter.

Type millimetres or inches and the other box updates as you type. One inch is exactly 25.4 mm, so inches = mm ÷ 25.4. For fractions of an inch, use the decimal-to-fraction tool. Runs in your browser; nothing is sent anywhere.

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Result

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Answer

25 mm is 0.9843 in. 1 in = 25.4 mm exactly, so 1 mm = 0.0393700787… in.

Formula

inches = mm ÷ 25.4

Take 25 mm. inches = mm ÷ 25.4 gives 0.9843 in. Going back: 0.9843 in converts back to 25 mm.

Quick estimate: divide millimetres by 25.

Mm to inches table (1 to 100)

Millimetres (mm)Inches (in)
10.0394
20.0787
30.1181
40.1575
50.1969
60.2362
70.2756
80.315
90.3543
100.3937
150.5906
200.7874
250.9843
301.1811
401.5748
501.9685
602.3622
702.7559
752.9528
803.1496
903.5433
1003.937

Examples

Source

Conversion factors and formulas: NIST SP 811, Appendix B.8: inch to meter 2.54 E-02 (so 1 in = 25.4 mm); NIST Handbook 44 (2026), Appendix C: 1 inch = 2.54 cm = 25.4 mm. Retrieved 2026-10. Results are rounded for display to 4 decimal places; the arithmetic itself is not rounded.

FAQ

How many inches are in 1 millimetre?

1 mm is 0.03937 in. 1 in = 25.4 mm exactly, so 1 mm = 0.0393700787… in.

What is the formula to convert millimetres to inches?

inches = mm ÷ 25.4. For 10 mm that gives 0.3937 in.

Is the conversion factor exact?

Yes for the stated definition. 1 in = 25.4 mm exactly, so 1 mm = 0.0393700787… in. The tool shows results rounded to four decimal places; the underlying arithmetic is not rounded.

How do I estimate it in my head?

Quick estimate: divide millimetres by 25. Use the exact factor when accuracy matters.

What is 25 mm in inches?

25 mm is 0.9843 in.

Disclaimer

Informational arithmetic using the published factors above. For legal-for-trade, engineering or medical use, check against the governing standard.

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