A drawing calls out 0.3125″, the drill index reads in fractions, and the customer asks for millimeters. They’re all the same size — this just saves you the math. Type a value into the converter for an instant answer, or scan the table for the standard fractions.
| Fraction | Decimal (in) | Millimeters |
|---|---|---|
| 1/64″ | 0.0156 | 0.40 |
| 1/32″ | 0.0312 | 0.79 |
| 3/64″ | 0.0469 | 1.19 |
| 1/16″ | 0.0625 | 1.59 |
| 5/64″ | 0.0781 | 1.98 |
| 3/32″ | 0.0938 | 2.38 |
| 7/64″ | 0.1094 | 2.78 |
| 1/8″ | 0.1250 | 3.17 |
| 9/64″ | 0.1406 | 3.57 |
| 5/32″ | 0.1562 | 3.97 |
| 11/64″ | 0.1719 | 4.37 |
| 3/16″ | 0.1875 | 4.76 |
| 13/64″ | 0.2031 | 5.16 |
| 7/32″ | 0.2188 | 5.56 |
| 15/64″ | 0.2344 | 5.95 |
| 1/4″ | 0.2500 | 6.35 |
| 17/64″ | 0.2656 | 6.75 |
| 9/32″ | 0.2812 | 7.14 |
| 19/64″ | 0.2969 | 7.54 |
| 5/16″ | 0.3125 | 7.94 |
| 21/64″ | 0.3281 | 8.33 |
| 11/32″ | 0.3438 | 8.73 |
| 23/64″ | 0.3594 | 9.13 |
| 3/8″ | 0.3750 | 9.52 |
| 25/64″ | 0.3906 | 9.92 |
| 13/32″ | 0.4062 | 10.32 |
| 27/64″ | 0.4219 | 10.72 |
| 7/16″ | 0.4375 | 11.11 |
| 29/64″ | 0.4531 | 11.51 |
| 15/32″ | 0.4688 | 11.91 |
| 31/64″ | 0.4844 | 12.30 |
| 1/2″ | 0.5000 | 12.70 |
| 33/64″ | 0.5156 | 13.10 |
| 17/32″ | 0.5312 | 13.49 |
| 35/64″ | 0.5469 | 13.89 |
| 9/16″ | 0.5625 | 14.29 |
| 37/64″ | 0.5781 | 14.68 |
| 19/32″ | 0.5938 | 15.08 |
| 39/64″ | 0.6094 | 15.48 |
| 5/8″ | 0.6250 | 15.88 |
| 41/64″ | 0.6406 | 16.27 |
| 21/32″ | 0.6562 | 16.67 |
| 43/64″ | 0.6719 | 17.07 |
| 11/16″ | 0.6875 | 17.46 |
| 45/64″ | 0.7031 | 17.86 |
| 23/32″ | 0.7188 | 18.26 |
| 47/64″ | 0.7344 | 18.65 |
| 3/4″ | 0.7500 | 19.05 |
| 49/64″ | 0.7656 | 19.45 |
| 25/32″ | 0.7812 | 19.84 |
| 51/64″ | 0.7969 | 20.24 |
| 13/16″ | 0.8125 | 20.64 |
| 53/64″ | 0.8281 | 21.03 |
| 27/32″ | 0.8438 | 21.43 |
| 55/64″ | 0.8594 | 21.83 |
| 7/8″ | 0.8750 | 22.22 |
| 57/64″ | 0.8906 | 22.62 |
| 29/32″ | 0.9062 | 23.02 |
| 59/64″ | 0.9219 | 23.42 |
| 15/16″ | 0.9375 | 23.81 |
| 61/64″ | 0.9531 | 24.21 |
| 31/32″ | 0.9688 | 24.61 |
| 63/64″ | 0.9844 | 25.00 |
| 1″ | 1.0000 | 25.40 |
One inch is exactly 25.4 mm. To go from inches to millimeters, multiply by 25.4; to go the other way, divide by 25.4. The converter above rounds the nearest fraction to the closest 1/64″.
