Tap Drill Size Calculator

A calculator that calculates size of a tap drill, nominal diameter of a number machine screw, and thread pitch.

### General Formula (65% - 75% Thread)

Drill Hole Size   Nominal or Basic
Diameter
Pitch
= -

Drill Hole
Size (in)
Outside
Diameter (in)
Percent
(decimal)
per Inch
= -  (1.08254  × / )

Drill Hole
Size (in)
Outside
Diameter (in)
Percent
(decimal)
per Inch
= -  (1.299  × / )

Drill Hole
Size (mm)
Outside
Diameter (mm)
Percent
(decimal)
Pitch (mm)
= -  (  1.08254  × × )

### Cold Form Tapping

Drill Hole
Size (in)
Outside
Diameter (in)
Percent
(decimal)
per Inch
= -  (  0.6800  × / )
Drill Hole
Size (mm)
Outside
Diameter (mm)
Percent
(decimal)
Pitch (mm)
= -  (0.6800  × × )

### Notes

Calculating Nominal Diameter of a Number Screw
Nominal
Diameter (in)
Screw Number
=   ( ×  0.0130)  +  0.0600

Calculating Pitch
Pitch ( )     Threads per Inch
= 1  /

Threads per Inch     Pitch ( )
= 1  /
Basic Diameter
The basic diameter is a numerical value used to describe the theoretical exact diameter.

Nominal Diameter
The nominal size is the designation which is used for the purpose of general identification.

Outside Diameter
The outside diameter is the largest diameter of a straight screw thread. The term has been replaced by "major diameter" which applies to both internal and external threads.

Author: Dawn Rorvik