Thread Pitch Calculator

Construction

Convert between threads per inch (TPI) and thread pitch (inches or mm).

Formula

Pitch (in) = 1/TPI; Pitch (mm) = 25.4/TPI; TPI = 1/pitch_in
  • Common UN pitches: 1/4-20=0.050 in, 3/8-16=0.0625 in, 1/2-13=0.0769 in, 3/4-10=0.1 in.
  • Common metric pitches: M4×0.7, M6×1.0, M8×1.25, M10×1.5 mm.

20 TPI

Inputs
  • Input Mode: tpi
  • Value: 20

20 TPI: pitch = 1/20 = 0.050 in = 1.270 mm. (Standard 1/4-20 UNC)

Frequently asked questions

What is TPI?
TPI (Threads Per Inch) is the number of thread crests in one inch measured along the bolt axis. It is the primary designation for Unified (imperial) threads.