MM to Inches Converter
Type millimeters to get inches, as a decimal and as the nearest fraction you would find on a ruler or drill set.
25 mm =
0.9843in
25 millimeters is 0.9843 inches.
- Nearest 1/16 inch
- 1 in
- 1 mm
- 0.03937 in
- 1 in
- 25.4 mm
How to convert mm to inches
Divide millimeters by 25.4, the exact number of millimeters in one inch. A 19 mm wrench works out at 19 ÷ 25.4 = 0.748 inches, only two thousandths of an inch under 3/4 inch (0.75).
To read the result as a fraction, multiply the decimal by 32 (or 64 for fine work) and round to a whole number. For 19 mm, 0.748 × 32 = 23.9, so about 24/32, which reduces to 3/4. For 10 mm, 0.3937 × 32 = 12.6, so 13/32 of an inch.
Very thin measurements are easier in thousandths of an inch: 0.1 mm is 0.003937 inch, roughly four thousandths of an inch.
inches = millimeters ÷ 25.4 (≈ millimeters × 0.0393701)
- NIST lists the inch as exactly 2.54 × 10⁻² meter, so one millimeter is 0.0393700787… inch, a decimal that never terminates. Source: NIST SP 811, Appendix B.8: conversion factors by unit.
How to estimate mm to inches in your head
Divide by 25 instead of 25.4: multiply by 4 and move the decimal point two places left. 6 mm × 4 = 24, so about 0.24 inch, while the exact figure is 0.2362. Dividing by 25 runs about 1.6% high.
Three anchors cover most hardware: 3 mm is close to 1/8 inch (0.118 versus 0.125), 6 mm is close to 1/4 inch (0.236 versus 0.25) and 13 mm is close to 1/2 inch (0.512 versus 0.5).
Millimeters to inches, with fractions
Sizes from 1 mm to 50 mm as decimal inches and the nearest thirty-second of an inch.
| Millimeters (mm) | Inches (decimal) | Nearest 1/32 inch |
|---|---|---|
| 1 | 0.03937 | 1/32 in |
| 2 | 0.07874 | 3/32 in |
| 3 | 0.1181 | 1/8 in |
| 4 | 0.1575 | 5/32 in |
| 5 | 0.1969 | 3/16 in |
| 6 | 0.2362 | 1/4 in |
| 8 | 0.315 | 5/16 in |
| 10 | 0.3937 | 13/32 in |
| 12 | 0.4724 | 15/32 in |
| 13 | 0.5118 | 1/2 in |
Show all 21 rowsShow fewer
| 15 | 0.5906 | 19/32 in |
| 16 | 0.6299 | 5/8 in |
| 19 | 0.748 | 3/4 in |
| 20 | 0.7874 | 25/32 in |
| 22 | 0.8661 | 7/8 in |
| 25 | 0.9843 | 31/32 in |
| 30 | 1.1811 | 1 3/16 in |
| 32 | 1.2598 | 1 1/4 in |
| 38 | 1.4961 | 1 1/2 in |
| 40 | 1.5748 | 1 9/16 in |
| 50 | 1.9685 | 1 31/32 in |
Frequently Asked Questions
How many inches is 10 mm?
10 mm is 0.3937 inch. To the nearest sixteenth that is 3/8 inch (0.375); to the nearest thirty-second it is 13/32 (0.406).
Is 19 mm the same as 3/4 inch?
Nearly. 3/4 inch is 19.05 mm, so a 19 mm socket is 0.05 mm smaller. That is why the two sizes are often swapped in a pinch, though a snug fit on a tight bolt can still slip.
How do I convert rainfall from mm to inches?
Divide by 25.4 as for any length. 25 mm of rain is 0.98 inch, so “an inch of rain” and “25 mm of rain” describe almost the same storm.