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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.
Drill Bit Size Conversion Methods
1. Convert Drill Bit mm to Inches
When drill bit diameter size is available in mm it can convert into inches easily.
Mathematically,
1mm = 0.0393701 inches.
When you need to convert mm to inches, you have to multiply the mm value by 0.0393701
Ex – 15.875 mm × 0.0393701 = 0.625000 inches = 5/8″
You can check fraction and decimal conversion using the below table. Practically, you may not be able to measure the drill bit diameter more than 2 decimal places. Hence measure it as much as possible accuracy.
2. Convert Drill Bit Inches to mm.
When you measure drill bit size in inches, you can convert it into mm using this method.
1 inch = 25.4mm
You can multiply by 25.4 of inches value when you convert that to mm.
Ex – 0.5 inches = 1/2″ = 0.5 inches × 25.4 = 12.7mm
Inches are really popular in the USA but, beyond that, mostly used 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.
Drill Bit Size Chart
By following the above method, this table has been prepared with available drill bit sizes. You can see fractions, inches, and mm values for each drill bit size here.
| 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 |
Measure Drill Bit Size
Remembering everything is not easy. As for me I use this gauge to quickly identify the drill bit size in inches and millimeters. This is IRWIN drill gauge. You can measure 1/16″ to 1/2″ range of drill bits using that gauge.
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