Fractional inches to millimetres
Every sixty-fourth from 1/64″ through 1″, reduced to its simplest fraction. One inch is exactly 25.4 mm, so these displayed conversions are exact.
Select a fraction to open the chart. It continues beyond this one-inch table, through the supported 0–200 mm range.
| Size Open on chart ↗ | Millimetres | Decimal inches |
|---|---|---|
| 1/64″ | 0.396875 | 0.015625″ |
| 1/32″ | 0.79375 | 0.03125″ |
| 3/64″ | 1.190625 | 0.046875″ |
| 1/16″ | 1.5875 | 0.0625″ |
| 5/64″ | 1.984375 | 0.078125″ |
| 3/32″ | 2.38125 | 0.09375″ |
| 7/64″ | 2.778125 | 0.109375″ |
| 1/8″ | 3.175 | 0.125″ |
| 9/64″ | 3.571875 | 0.140625″ |
| 5/32″ | 3.96875 | 0.15625″ |
| 11/64″ | 4.365625 | 0.171875″ |
| 3/16″ | 4.7625 | 0.1875″ |
| 13/64″ | 5.159375 | 0.203125″ |
| 7/32″ | 5.55625 | 0.21875″ |
| 15/64″ | 5.953125 | 0.234375″ |
| 1/4″ | 6.35 | 0.25″ |
| 17/64″ | 6.746875 | 0.265625″ |
| 9/32″ | 7.14375 | 0.28125″ |
| 19/64″ | 7.540625 | 0.296875″ |
| 5/16″ | 7.9375 | 0.3125″ |
| 21/64″ | 8.334375 | 0.328125″ |
| 11/32″ | 8.73125 | 0.34375″ |
| 23/64″ | 9.128125 | 0.359375″ |
| 3/8″ | 9.525 | 0.375″ |
| 25/64″ | 9.921875 | 0.390625″ |
| 13/32″ | 10.31875 | 0.40625″ |
| 27/64″ | 10.715625 | 0.421875″ |
| 7/16″ | 11.1125 | 0.4375″ |
| 29/64″ | 11.509375 | 0.453125″ |
| 15/32″ | 11.90625 | 0.46875″ |
| 31/64″ | 12.303125 | 0.484375″ |
| 1/2″ | 12.7 | 0.5″ |
| 33/64″ | 13.096875 | 0.515625″ |
| 17/32″ | 13.49375 | 0.53125″ |
| 35/64″ | 13.890625 | 0.546875″ |
| 9/16″ | 14.2875 | 0.5625″ |
| 37/64″ | 14.684375 | 0.578125″ |
| 19/32″ | 15.08125 | 0.59375″ |
| 39/64″ | 15.478125 | 0.609375″ |
| 5/8″ | 15.875 | 0.625″ |
| 41/64″ | 16.271875 | 0.640625″ |
| 21/32″ | 16.66875 | 0.65625″ |
| 43/64″ | 17.065625 | 0.671875″ |
| 11/16″ | 17.4625 | 0.6875″ |
| 45/64″ | 17.859375 | 0.703125″ |
| 23/32″ | 18.25625 | 0.71875″ |
| 47/64″ | 18.653125 | 0.734375″ |
| 3/4″ | 19.05 | 0.75″ |
| 49/64″ | 19.446875 | 0.765625″ |
| 25/32″ | 19.84375 | 0.78125″ |
| 51/64″ | 20.240625 | 0.796875″ |
| 13/16″ | 20.6375 | 0.8125″ |
| 53/64″ | 21.034375 | 0.828125″ |
| 27/32″ | 21.43125 | 0.84375″ |
| 55/64″ | 21.828125 | 0.859375″ |
| 7/8″ | 22.225 | 0.875″ |
| 57/64″ | 22.621875 | 0.890625″ |
| 29/32″ | 23.01875 | 0.90625″ |
| 59/64″ | 23.415625 | 0.921875″ |
| 15/16″ | 23.8125 | 0.9375″ |
| 61/64″ | 24.209375 | 0.953125″ |
| 31/32″ | 24.60625 | 0.96875″ |
| 63/64″ | 25.003125 | 0.984375″ |
| 1″ | 25.4 | 1″ |
Exact conversions, without rounding away the difference
Multiply a dimension in inches by 25.4 to express it in millimetres. For 1/64″, that gives 0.015625″ and 0.396875 mm exactly. The table keeps six decimal places where needed.
These are dimensions. A matching fractional dimension does not by itself establish a thread fit or a suitable tapping drill. The drill size chart lists the actual drill designations separately.
Sources & scope
Data edition 1.0. Values come from the reference sources below. SizeAxis is a selected reference catalogue; it does not certify manufactured dimensions or thread compatibility.
Read the measurement definitions and full coverage