Tap Drill Calculator

Tap Drill Size

Live Calculation

Select the tap type, tap size, and desired percentage of full thread. All results update immediately.

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Select a Tap Setup
The calculated hole and closest drill sizes will appear here.
Calculation Basis

The tap selections and drill table are taken from the original Machinist Companion Lite data tables. Cut-tap and form-tap hole sizes use the four formulas from the original TapHoleCalcScreen logic.

The theoretical hole is compared with the sorted drill table. An exact diameter match displays one drill. Otherwise, the closest drill below and above the theoretical size are displayed, together with the calculated percentage of full thread each drill would produce.

No thread-percentage recommendation is made by this tool. The selected percentage is treated only as an input to the calculation.

Engineering reference only. Verify critical dimensions, parameters, machine/tool limits and governing specifications before use. Terms & Disclaimer