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Tap Drill Calculator
Metric rule of thumb: tap drill = major diameter − pitch. Enter D and P above for the exact value.
Metric Coarse Tap Drill Chart
| Thread | Pitch (mm) | Tap drill (mm) | Nearest drill |
|---|---|---|---|
| M3 | 0.5 | 2.5 | 2.5 mm |
| M4 | 0.7 | 3.3 | 3.5 mm |
| M5 | 0.8 | 4.2 | 4.0 mm |
| M6 | 1.0 | 5.0 | 5.0 mm |
| M8 | 1.25 | 6.75 | 7.0 mm |
| M10 | 1.5 | 8.5 | 8.5 mm |
| M12 | 1.75 | 10.25 | 10.0 mm |
| M16 | 2.0 | 14.0 | 14.0 mm |
| M20 | 2.5 | 17.5 | 17.5 mm |
| M24 | 3.0 | 21.0 | 21.0 mm |
UNC Tap Drill Chart
| Thread | TPI | Tap drill (in) | Tap drill (mm) |
|---|---|---|---|
| 1/4-20 | 20 | #7 (0.201) | 5.1 |
| 5/16-18 | 18 | F (0.257) | 6.5 |
| 3/8-16 | 16 | 5/16 (0.3125) | 8.0 |
| 1/2-13 | 13 | 3/8 (0.375) | 9.5 |
| 5/8-11 | 11 | 17/32 (0.531) | 13.5 |
| 3/4-10 | 10 | 21/32 (0.656) | 16.7 |
| 1-8 | 8 | 7/8 (0.875) | 22.2 |
FAQ
What percentage thread should I tap for?
75% is the industry standard for steel — nearly full strength with much less torque than 100%.
What is the metric tap drill formula?
Tap drill (mm) = major diameter (mm) − pitch (mm).