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Every sixty-fourth of an inch as an exact decimal and in millimetres, the common fractions as decimals and percentages, and how to convert in both directions. Sixty-fourths are the divisions on a standard imperial rule and the usual steps in drill and fastener sizes.
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Sixty-fourths of an inch, exact decimals, exact millimetres.
| Inch | Decimal | mm |
|---|---|---|
| 1/64 | 0.015625 | 0.397 |
| 1/32 | 0.03125 | 0.794 |
| 3/64 | 0.046875 | 1.191 |
| 1/16 | 0.0625 | 1.588 |
| 5/64 | 0.078125 | 1.984 |
| 3/32 | 0.09375 | 2.381 |
| 7/64 | 0.109375 | 2.778 |
| 1/8 | 0.125 | 3.175 |
| 9/64 | 0.140625 | 3.572 |
| 5/32 | 0.15625 | 3.969 |
| 11/64 | 0.171875 | 4.366 |
| 3/16 | 0.1875 | 4.762 |
| 13/64 | 0.203125 | 5.159 |
| 7/32 | 0.21875 | 5.556 |
| 15/64 | 0.234375 | 5.953 |
| 1/4 | 0.25 | 6.350 |
| 17/64 | 0.265625 | 6.747 |
| 9/32 | 0.28125 | 7.144 |
| 19/64 | 0.296875 | 7.541 |
| 5/16 | 0.3125 | 7.938 |
| 21/64 | 0.328125 | 8.334 |
| 11/32 | 0.34375 | 8.731 |
| 23/64 | 0.359375 | 9.128 |
| 3/8 | 0.375 | 9.525 |
| 25/64 | 0.390625 | 9.922 |
| 13/32 | 0.40625 | 10.319 |
| 27/64 | 0.421875 | 10.716 |
| 7/16 | 0.4375 | 11.112 |
| 29/64 | 0.453125 | 11.509 |
| 15/32 | 0.46875 | 11.906 |
| 31/64 | 0.484375 | 12.303 |
| 1/2 | 0.5 | 12.700 |
| 33/64 | 0.515625 | 13.097 |
| 17/32 | 0.53125 | 13.494 |
| 35/64 | 0.546875 | 13.891 |
| 9/16 | 0.5625 | 14.288 |
| 37/64 | 0.578125 | 14.684 |
| 19/32 | 0.59375 | 15.081 |
| 39/64 | 0.609375 | 15.478 |
| 5/8 | 0.625 | 15.875 |
| 41/64 | 0.640625 | 16.272 |
| 21/32 | 0.65625 | 16.669 |
| 43/64 | 0.671875 | 17.066 |
| 11/16 | 0.6875 | 17.462 |
| 45/64 | 0.703125 | 17.859 |
| 23/32 | 0.71875 | 18.256 |
| 47/64 | 0.734375 | 18.653 |
| 3/4 | 0.75 | 19.050 |
| 49/64 | 0.765625 | 19.447 |
| 25/32 | 0.78125 | 19.844 |
| 51/64 | 0.796875 | 20.241 |
| 13/16 | 0.8125 | 20.638 |
| 53/64 | 0.828125 | 21.034 |
| 27/32 | 0.84375 | 21.431 |
| 55/64 | 0.859375 | 21.828 |
| 7/8 | 0.875 | 22.225 |
| 57/64 | 0.890625 | 22.622 |
| 29/32 | 0.90625 | 23.019 |
| 59/64 | 0.921875 | 23.416 |
| 15/16 | 0.9375 | 23.812 |
| 61/64 | 0.953125 | 24.209 |
| 31/32 | 0.96875 | 24.606 |
| 63/64 | 0.984375 | 25.003 |
| 1 | 1 | 25.400 |
Read down each block of three columns, then across to the next block. Every decimal here is exact and stops: a fraction over 64 always does.
| Fraction | Decimal | Percent | mm |
|---|---|---|---|
| 1/2 | 0.5 | 50% | 12.700 |
| 1/3 | 0.3333… | 33.33…% | 8.467 |
| 2/3 | 0.6666… | 66.66…% | 16.933 |
| 1/4 | 0.25 | 25% | 6.350 |
| 3/4 | 0.75 | 75% | 19.050 |
| 1/5 | 0.2 | 20% | 5.080 |
| 2/5 | 0.4 | 40% | 10.160 |
| 4/5 | 0.8 | 80% | 20.320 |
| 1/6 | 0.1666… | 16.66…% | 4.233 |
| 5/6 | 0.8333… | 83.33…% | 21.167 |
| 1/8 | 0.125 | 12.5% | 3.175 |
| 3/8 | 0.375 | 37.5% | 9.525 |
| 5/8 | 0.625 | 62.5% | 15.875 |
| 7/8 | 0.875 | 87.5% | 22.225 |
| 1/10 | 0.1 | 10% | 2.540 |
| 1/16 | 0.0625 | 6.25% | 1.588 |
A tail of dots means the digits repeat for ever. One third is 0.3333 and onwards; it never stops and never settles.
| Fraction to decimal | Divide top by bottom: 3/8 is 3 / 8 = 0.375. |
| Decimal to percent | Multiply by 100: 0.375 becomes 37.5%. |
| Inches to millimetres | Multiply by 25.4, a figure that is exact. |
| Millimetres to inches | Divide by 25.4: 10 mm is 0.3937 inches. |
| Every decimal here stops | A fraction over 64 always terminates. |
| Halving a fraction | doubles the bottom: half of 1/8 is 1/16. |
The millimetre column uses 25.4 millimetres to the inch, which is exact by the international yard and pound agreement of 1959, rounded only at the last step to three places.
Sixty-fourths are the divisions on a standard imperial rule and the usual steps in drill and fastener sizes, which is why the big table runs in 64ths rather than 16ths.
To go the other way, divide millimetres by 25.4: 10 mm is 0.3937 inches, a shade under 25/64.