Last updated: December 26, 2025
Metric to SAE calculator explained
If you work with tools that mix metric sizes and fractional inches, you often need a fast bridge between mm and SAE-style inches. This calculator converts millimeters to decimal inches and also shows a fractional inch value rounded to the nearest 1/64.
How the conversion works
The inch is defined exactly:
So the base conversion is:
The fractional inch display rounds the decimal inch value to a nearby fraction with denominator up to 64.
Units and conversions
| Unit | Symbol | Relation |
|---|---|---|
| Millimeter | mm | |
| Inch | in | |
| Fractional inch | in (fraction) | rounded representation of inches |
Worked examples
-
Converting 12.7 mm to inches
Result: 0.5 in, which is 1/2 in in fractional form.
-
Converting 25 mm to inches
Result: 0.984252 in; the nearest 1/64 is 63/64 in (0.984375 in).
Tips and pitfalls
- Fractional rounding can hide small differences; use decimal inches when tolerance matters.
- Many common tool sizes are not exact conversions. Treat "nearest SAE size" as a convenience, not a guarantee of fit.
- If you already have inches, switch to the fractional inch view for a readable shop format.