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Drill bits are available in different materials, lengths, and diameters. Most are measured by the metric units and in the USA it’s imperial units. Drill bit diameter is the most important factor in the drilling process and it should know precisely as much as possible to sharpen or tolerate the diameter.
All over the world, one of the metric or imperial units is used as the general unit. When you use this you have to convert each with different units types.
1 inch is equal to 25.4 mm. By dividing the inches other fractions are introduced. Inches are really popular in the USA but beyond that mostly used the SI units. So we have to interchange the metric units and imperial units.
The below table will introduce you to the fractions and decimals of the inches with mm.
1 inch = 2.54 cm = 25.4 mm
| Fraction | inch | mm |
| 1⁄64 | 0.015625 | 0.396875 |
| 1⁄32 | 0.03125 | 0.79375 |
| 3⁄64 | 0.046875 | 1.190625 |
| 1⁄16 | 0.0625 | 1.5875 |
| 5⁄64 | 0.078125 | 1.984375 |
| 3⁄32 | 0.09375 | 2.38125 |
| 7⁄64 | 0.109375 | 2.778125 |
| 1⁄8 | 0.125 | 3.175 |
| 9⁄64 | 0.140625 | 3.571875 |
| 5⁄32 | 0.15625 | 3.96875 |
| 11⁄64 | 0.171875 | 4.365625 |
| 3⁄16 | 0.1875 | 4.7625 |
| 13⁄64 | 0.203125 | 5.159375 |
| 7⁄32 | 0.21875 | 5.55625 |
| 15⁄64 | 0.234375 | 5.953125 |
| 1⁄4 | 0.25 | 6.35 |
| 17⁄64 | 0.265625 | 6.746875 |
| 9⁄32 | 0.28125 | 7.14375 |
| 19⁄64 | 0.296875 | 7.540625 |
| 5⁄16 | 0.3125 | 7.9375 |
| 21⁄64 | 0.328125 | 8.334375 |
| 11⁄32 | 0.34375 | 8.73125 |
| 23⁄64 | 0.359375 | 9.128125 |
| 3⁄8 | 0.375 | 9.525 |
| 25⁄64 | 0.390625 | 9.921875 |
| 13⁄32 | 0.40625 | 10.31875 |
| 27⁄64 | 0.421875 | 10.715625 |
| 7⁄16 | 0.4375 | 11.1125 |
| 29⁄64 | 0.453125 | 11.509375 |
| 15⁄32 | 0.46875 | 11.90625 |
| 31⁄64 | 0.484375 | 12.303125 |
| 33⁄64 | 0.515625 | 13.096875 |
| 17⁄32 | 0.53125 | 13.49375 |
| 35⁄64 | 0.546875 | 13.890625 |
| 9⁄16 | 0.5625 | 14.2875 |
| 37⁄64 | 0.578125 | 14.684375 |
| 19⁄32 | 0.59375 | 15.08125 |
| 39⁄64 | 0.609375 | 15.478125 |
| 5⁄8 | 0.625 | 15.875 |
| 41⁄64 | 0.640625 | 16.271875 |
| 21⁄32 | 0.65625 | 16.66875 |
| 43⁄64 | 0.671875 | 17.065625 |
| 11⁄16 | 0.6875 | 17.4625 |
| 45⁄64 | 0.703125 | 17.859375 |
| 23⁄32 | 0.71875 | 18.25625 |
| 47⁄64 | 0.734375 | 18.653125 |
| 3⁄4 | 0.75 | 19.05 |
| 49⁄64 | 0.765625 | 19.446875 |
| 25⁄32 | 0.78125 | 19.84375 |
| 51⁄64 | 0.796875 | 20.240625 |
| 13⁄16 | 0.8125 | 20.6375 |
| 53⁄64 | 0.828125 | 21.034375 |
| 27⁄32 | 0.84375 | 21.43125 |
| 55⁄64 | 0.859375 | 21.828125 |
| 7⁄8 | 0.875 | 22.225 |
| 57⁄64 | 0.890625 | 22.621875 |
| 29⁄32 | 0.90625 | 23.01875 |
| 59⁄64 | 0.921875 | 23.415625 |
| 15⁄16 | 0.9375 | 23.8125 |
| 61⁄64 | 0.953125 | 24.209375 |
| 31⁄32 | 0.96875 | 24.60625 |
| 63⁄64 | 0.984375 | 25.003125 |
| 1 | 1 | 25.4 |
Remembering everything is not easy. As for me I use this gauge to quickly identfy the drill bit size in inches and milimeters.
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