MM to Inches Converter
Enter one length in millimeters. Choose decimal inches for a drawing or a fraction for an inch ruler. When a fraction is only a nearby match, the tool shows the difference rather than treating it as the same size.
Convert your millimeter measurement
Enter one nonnegative number, such as 6, 10 or 25.4.
Automatic keeps up to 6 decimals. Choose a fraction your ruler actually shows.
Decimal inches
25.4 mm ÷ 25.4 = 1 in
This decimal result is exact.
Where does 10 mm fall on an inch ruler?
10 mm is about 0.393701 inches. On a ruler marked in sixteenths, the nearest mark is 3/8 inch, which is 9.525 mm. That mark is 0.475 mm shorter than the original length.
With sixty-fourths, the nearest mark is 25/64 inch, or 9.921875 mm. The difference shrinks to 0.078125 mm, but it is still not exact. Select your ruler's divisions above to see that difference for your own measurement.
Millimeters to inches conversion chart
Decimal values use up to four places. Fractions use the nearest 1/16 inch. The = sign marks an exact match; ≈ marks a rounded one. Change the fraction setting in the calculator for a finer ruler.
Open the copyable text table
| mm | Decimal inches | Nearest 1/16 in |
|---|---|---|
| 1 | ≈ 0.0394 | ≈ 1/16 |
| 3 | ≈ 0.1181 | ≈ 1/8 |
| 6 | ≈ 0.2362 | ≈ 1/4 |
| 6.35 | = 0.25 | = 1/4 |
| 10 | ≈ 0.3937 | ≈ 3/8 |
| 12.7 | = 0.5 | = 1/2 |
| 19.05 | = 0.75 | = 3/4 |
| 25.4 | = 1 | = 1 |
| 50 | ≈ 1.9685 | ≈ 1 15/16 |
| 100 | ≈ 3.937 | ≈ 3 15/16 |
Keep decimal inches when the drawing needs them
The conversion is inches = millimeters ÷ 25.4. The factor is exact, but many answers have repeating decimals: 1 mm is approximately 0.039370079 inches. More digits do not improve the original measurement.
For a drawing or CAD entry, use the decimal result and keep the original millimeter dimension available. Match the required precision to the drawing's tolerance, not to a convenient ruler fraction. Very small or large decimal results use scientific notation.
Definition: NIST's international inch reference gives 1 inch = 25.4 mm exactly. Fraction results round to the nearest selected division; halfway values round upward. The difference shown is the ruler mark minus your original length.