CONVERSION · EN
mm to inches (mm → in) with fractions
Convert millimetres to decimal inches and 1/8 to 1/64 fractions. 1 inch equals exactly 25.4 mm.
Guide
Formula
inches = millimetres ÷ 25.4
The international inch is defined as exactly 25.4 mm. Calculation preserves this definition; the displayed decimal is rounded to the selected precision, and the fraction to the selected step. These roundings are distinct from physical measurement uncertainty. The optional limit applies only to the fraction error.
Note : For a mechanical dimension, use the decimal value and the drawing tolerance rather than a nearby fraction.
Example : 19 mm
Common conversions
Display rounded to at most 6 decimal places.
| mm | in |
|---|---|
| 1 | 0.03937 |
| 5 | 0.19685 |
| 10 | 0.393701 |
| 19 | 0.748031 |
| 25.4 | 1 |
| 50 | 1.968504 |
| 100 | 3.937008 |
Related conversions
Definition sources
Measurement
Enter a value and its unit.
Calculation details and sources are available below the result.
Enter a measurement: its unit is detected automatically.
Useful conversions
Approximate fraction
This approximation certifies neither a part nor an instrument’s accuracy.
Fractions and precision
| Step | Fraction | Error in mm | Limit |
|---|
Error = approximate fraction − requested measurement. Exact comparison before display rounding.
A list
One measurement per line. The unit is detected independently on every line, including common typos.
Applies only to numbers without a unit. Written units always take precedence.
For bare numbers, choose their common unit. No unit is guessed.
No results.
Add your measurements, choose the targets, then convert.
| Line | Original | Detected | To | Result | Status |
|---|