Reference & Charts
Fraction, Decimal & Millimetre Chart
Every 1/64" step from 1/64" to 1", with the decimal-inch and millimetre equivalent for each. Convert a fractional call-out to the decimal your caliper reads or the millimetres your CAD model uses. Search a fraction (3/8), a decimal (0.375), or a millimetre value.
64 entries · Last verified: 2026-07-22
Drawings call out inch fractions, calipers and DROs read decimal inches, and CAD/CAM works in millimetres — so the same dimension gets converted a dozen times a day. This chart lists every 1/64" step with both equivalents. The decimal is simply the fraction's value, and the millimetre figure is that decimal multiplied by 25.4, so every number is exact.
Showing 64 of 64
| Conversion | Fraction | Decimal inch(in) | Millimetres(mm) |
|---|---|---|---|
| 1/64" | 1/64" | 0.0156 in | 0.3969 mm |
| 1/32" | 1/32" | 0.0313 in | 0.7938 mm |
| 3/64" | 3/64" | 0.0469 in | 1.1906 mm |
| 1/16" | 1/16" | 0.0625 in | 1.5875 mm |
| 5/64" | 5/64" | 0.0781 in | 1.9844 mm |
| 3/32" | 3/32" | 0.0938 in | 2.3812 mm |
| 7/64" | 7/64" | 0.1094 in | 2.7781 mm |
| 1/8" | 1/8" | 0.125 in | 3.175 mm |
| 9/64" | 9/64" | 0.1406 in | 3.5719 mm |
| 5/32" | 5/32" | 0.1563 in | 3.9688 mm |
| 11/64" | 11/64" | 0.1719 in | 4.3656 mm |
| 3/16" | 3/16" | 0.1875 in | 4.7625 mm |
| 13/64" | 13/64" | 0.2031 in | 5.1594 mm |
| 7/32" | 7/32" | 0.2188 in | 5.5562 mm |
| 15/64" | 15/64" | 0.2344 in | 5.9531 mm |
| 1/4" | 1/4" | 0.25 in | 6.35 mm |
| 17/64" | 17/64" | 0.2656 in | 6.7469 mm |
| 9/32" | 9/32" | 0.2813 in | 7.1438 mm |
| 19/64" | 19/64" | 0.2969 in | 7.5406 mm |
| 5/16" | 5/16" | 0.3125 in | 7.9375 mm |
| 21/64" | 21/64" | 0.3281 in | 8.3344 mm |
| 11/32" | 11/32" | 0.3438 in | 8.7313 mm |
| 23/64" | 23/64" | 0.3594 in | 9.1281 mm |
| 3/8" | 3/8" | 0.375 in | 9.525 mm |
| 25/64" | 25/64" | 0.3906 in | 9.9219 mm |
| 13/32" | 13/32" | 0.4063 in | 10.3188 mm |
| 27/64" | 27/64" | 0.4219 in | 10.7156 mm |
| 7/16" | 7/16" | 0.4375 in | 11.1125 mm |
| 29/64" | 29/64" | 0.4531 in | 11.5094 mm |
| 15/32" | 15/32" | 0.4688 in | 11.9063 mm |
| 31/64" | 31/64" | 0.4844 in | 12.3031 mm |
| 1/2" | 1/2" | 0.5 in | 12.7 mm |
| 33/64" | 33/64" | 0.5156 in | 13.0969 mm |
| 17/32" | 17/32" | 0.5313 in | 13.4938 mm |
| 35/64" | 35/64" | 0.5469 in | 13.8906 mm |
| 9/16" | 9/16" | 0.5625 in | 14.2875 mm |
| 37/64" | 37/64" | 0.5781 in | 14.6844 mm |
| 19/32" | 19/32" | 0.5938 in | 15.0813 mm |
| 39/64" | 39/64" | 0.6094 in | 15.4781 mm |
| 5/8" | 5/8" | 0.625 in | 15.875 mm |
| 41/64" | 41/64" | 0.6406 in | 16.2719 mm |
| 21/32" | 21/32" | 0.6563 in | 16.6688 mm |
| 43/64" | 43/64" | 0.6719 in | 17.0656 mm |
| 11/16" | 11/16" | 0.6875 in | 17.4625 mm |
| 45/64" | 45/64" | 0.7031 in | 17.8594 mm |
| 23/32" | 23/32" | 0.7188 in | 18.2562 mm |
| 47/64" | 47/64" | 0.7344 in | 18.6531 mm |
| 3/4" | 3/4" | 0.75 in | 19.05 mm |
| 49/64" | 49/64" | 0.7656 in | 19.4469 mm |
| 25/32" | 25/32" | 0.7813 in | 19.8438 mm |
| 51/64" | 51/64" | 0.7969 in | 20.2406 mm |
| 13/16" | 13/16" | 0.8125 in | 20.6375 mm |
| 53/64" | 53/64" | 0.8281 in | 21.0344 mm |
| 27/32" | 27/32" | 0.8438 in | 21.4313 mm |
| 55/64" | 55/64" | 0.8594 in | 21.8281 mm |
| 7/8" | 7/8" | 0.875 in | 22.225 mm |
| 57/64" | 57/64" | 0.8906 in | 22.6219 mm |
| 29/32" | 29/32" | 0.9063 in | 23.0187 mm |
| 59/64" | 59/64" | 0.9219 in | 23.4156 mm |
| 15/16" | 15/16" | 0.9375 in | 23.8125 mm |
| 61/64" | 61/64" | 0.9531 in | 24.2094 mm |
| 31/32" | 31/32" | 0.9688 in | 24.6063 mm |
| 63/64" | 63/64" | 0.9844 in | 25.0031 mm |
| 1" | 1" | 1 in | 25.4 mm |
Frequently asked
- How do I convert an inch fraction to millimetres?
- Divide the fraction to get its decimal value, then multiply by 25.4. Example: 3/8" = 0.375", and 0.375 × 25.4 = 9.525 mm. Every row here lists both so you don't have to.
- Why is 25.4 the number?
- One inch is defined as exactly 25.4 millimetres (international inch, 1959). Because the definition is exact, every inch-to-millimetre conversion here is exact, not rounded from a physical measurement.
- Are the decimals rounded?
- The decimal-inch and millimetre columns are shown to four decimal places, which is finer than any shop tolerance you'd hold to a fraction. The underlying values are computed from the exact fraction, so the rounding is display-only.
Sources
- Exact arithmetic: decimal inch = the fraction's value; millimetres = decimal inch × 25.4
- International inch definition: 1 in = 25.4 mm exactly (1959)