Tap Drill Sizes

The general rule of thumb for tap drill sizes (with 75% thread engagement) is to take the diameter (e.g. 10 mm) and subtract the pitch (e.g. 1.5 mm), giving the tap drill size (e.g. 8.5 mm). However, in some cases it is useful to either reduce the thread engagement (for example when tapping in hard materials) or increase it (for example when tapping thin materials).

This calculator allows you to adjust the thread engagement percentage and see the corresponding tap drill sizes for thread cutting and thread forming taps.

Thread Engagement (%):
Custom Thread Diameter (millimetres):
Custom Pitch (millimetres):
Show Only Coarse Threads:

Thread Cutting Taps:


Thread Forming Taps: