Every sixty-fourth of an inch as a decimal and in millimetres. A drawing that says 7/16 and a micrometer that reads 0.4375 are describing the same size; this table keeps the two in step.
Fractions are reduced. The sixteenths and thirty-seconds most often seen on drawings all appear in this list.
| Fraction (in) | Decimal (in) | Millimetres |
|---|---|---|
| 1/64 | 0.015625 | 0.3969 |
| 1/32 | 0.031250 | 0.7937 |
| 3/64 | 0.046875 | 1.1906 |
| 1/16 | 0.062500 | 1.5875 |
| 5/64 | 0.078125 | 1.9844 |
| 3/32 | 0.093750 | 2.3812 |
| 7/64 | 0.109375 | 2.7781 |
| 1/8 | 0.125000 | 3.1750 |
| 9/64 | 0.140625 | 3.5719 |
| 5/32 | 0.156250 | 3.9688 |
| 11/64 | 0.171875 | 4.3656 |
| 3/16 | 0.187500 | 4.7625 |
| 13/64 | 0.203125 | 5.1594 |
| 7/32 | 0.218750 | 5.5562 |
| 15/64 | 0.234375 | 5.9531 |
| 1/4 | 0.250000 | 6.3500 |
| 17/64 | 0.265625 | 6.7469 |
| 9/32 | 0.281250 | 7.1437 |
| 19/64 | 0.296875 | 7.5406 |
| 5/16 | 0.312500 | 7.9375 |
| 21/64 | 0.328125 | 8.3344 |
| 11/32 | 0.343750 | 8.7312 |
| 23/64 | 0.359375 | 9.1281 |
| 3/8 | 0.375000 | 9.5250 |
| 25/64 | 0.390625 | 9.9219 |
| 13/32 | 0.406250 | 10.3187 |
| 27/64 | 0.421875 | 10.7156 |
| 7/16 | 0.437500 | 11.1125 |
| 29/64 | 0.453125 | 11.5094 |
| 15/32 | 0.468750 | 11.9062 |
| 31/64 | 0.484375 | 12.3031 |
| 1/2 | 0.500000 | 12.7000 |
| 33/64 | 0.515625 | 13.0969 |
| 17/32 | 0.531250 | 13.4937 |
| 35/64 | 0.546875 | 13.8906 |
| 9/16 | 0.562500 | 14.2875 |
| 37/64 | 0.578125 | 14.6844 |
| 19/32 | 0.593750 | 15.0812 |
| 39/64 | 0.609375 | 15.4781 |
| 5/8 | 0.625000 | 15.8750 |
| 41/64 | 0.640625 | 16.2719 |
| 21/32 | 0.656250 | 16.6687 |
| 43/64 | 0.671875 | 17.0656 |
| 11/16 | 0.687500 | 17.4625 |
| 45/64 | 0.703125 | 17.8594 |
| 23/32 | 0.718750 | 18.2562 |
| 47/64 | 0.734375 | 18.6531 |
| 3/4 | 0.750000 | 19.0500 |
| 49/64 | 0.765625 | 19.4469 |
| 25/32 | 0.781250 | 19.8438 |
| 51/64 | 0.796875 | 20.2406 |
| 13/16 | 0.812500 | 20.6375 |
| 53/64 | 0.828125 | 21.0344 |
| 27/32 | 0.843750 | 21.4312 |
| 55/64 | 0.859375 | 21.8281 |
| 7/8 | 0.875000 | 22.2250 |
| 57/64 | 0.890625 | 22.6219 |
| 29/32 | 0.906250 | 23.0187 |
| 59/64 | 0.921875 | 23.4156 |
| 15/16 | 0.937500 | 23.8125 |
| 61/64 | 0.953125 | 24.2094 |
| 31/32 | 0.968750 | 24.6062 |
| 63/64 | 0.984375 | 25.0031 |
| 1 | 1.000000 | 25.4000 |
1/8 is 0.1250 as a decimal, and 3.1750 mm. Divide the top number by the bottom number to get the decimal.
5/16 is 0.3125, which is 7.9375 mm. It sits between 1/4 (0.2500) and 3/8 (0.3750).
Sixty-four. That is why 1/64 is the smallest division on a standard inch rule and why machinists work in thousandths once the fraction gets finer than that.
0.375 is 3/8, which is 9.5250 mm. Multiply the decimal by 64 and reduce: 0.375 x 64 = 24, and 24/64 reduces to 3/8.