Tap Drill Calculator
Cut and roll-form tap drills at any percent of thread — with the nearest standard drills and what each actually gives you.
Results
Nearest standard drills
| Drill | System | Decimal (in) | mm | % thread it gives |
|---|
Why not 75%? Above ~70–75% thread, tapping torque climbs fast while thread strength barely improves.
60–70% is plenty for most work in decent material; going finer than that mostly just breaks taps.
Roll-form taps displace material instead of cutting it, so they need a larger hole for the same percentage.
Full write-up: Tap Drill Size & Percent of Thread, Explained.