Inches to Fraction Calculator
Turn decimal inches into a tape-measure fraction, and see exactly how much you rounded.
At every denominator
| Precision | Fraction | Error |
|---|---|---|
| Nearest 1/2 | 3 1/2 in | -4.763 mm |
| Nearest 1/4 | 3 3/4 in | 1.588 mm |
| Nearest 1/8 | 3 3/4 in | 1.588 mm |
| Nearest 1/16 | 3 11/16 in | 0 mm |
| Nearest 1/32 | 3 11/16 in | 0 mm |
| Nearest 1/64 | 3 11/16 in | 0 mm |
How the rounding works
To express a decimal as a fraction with denominator d, multiply by d, round to a whole number, and put it back over d:
3.6875 × 16 = 59 → 59/16 = 3 11/16
The fraction is then reduced by dividing top and bottom by their greatest common divisor, so 8/16 becomes 1/2.
Why the error column matters
Sixteenths of an inch are about 1.6 mm apart, so rounding to the nearest sixteenth can be off by up to 0.8 mm. That is invisible on a single cut and very visible after twenty of them. If your measurement came from a metric drawing, consider keeping the millimetres and marking directly rather than converting.
Common decimals
0.125 = 1/8, 0.25 = 1/4, 0.375 = 3/8,
0.5 = 1/2, 0.625 = 5/8, 0.75 = 3/4,
0.875 = 7/8. These are exact — anything else is being rounded.