Tap Drill Size Calculator – Unified (UN) – Conventional

This calculator uses the conventional method. This is the method used by most calculators and the one that is used to generate most tap drill tables. This method gives the ratio in percent of the actual height of thread to the height of the obsolete American National Thread Profile. This height is different from the Unified Thread profile, but for consistency, this convention is retained in most tables. See FED-STD-H28-2B Section 20.2.3 and ASME B1.1.

See also: Unified Screw Threads.

Major Diameter: inches

Percent Full Thread: Enter as Percent (75 for 75%)

Threads Per Inch: TPI

Tap Drill Size: inches

This is the conventional method of calculating tap drill sizes.

This calculator uses the following formula:


FED-STD-H28-2B Section 20.2.3

ASME B1.1.