Thread Pitch Calculator

Convert between threads per inch (TPI) and thread pitch in millimeters or inches. Enter any one and see all three, in your browser.

-

Show the math

Threads per inch (TPI) and pitch describe the same thing from opposite directions: TPI counts threads in one inch, while pitch is the distance between adjacent threads.

pitch (inch) = 1 ÷ TPI

pitch (mm) = 25.4 ÷ TPI

Imperial threads (UNC/UNF) are specified in TPI; metric threads (M-series) are specified directly in millimeters of pitch.

What this does

This calculator converts between threads per inch (TPI) and thread pitch in millimeters or inches. Enter any one value and see all three at once.

How to use it

  1. Enter TPI, or a pitch in mm or inches.
  2. Read the other two values instantly.
  3. Use TPI for imperial, pitch for metric threads.

How it works

Pitch is the distance between adjacent threads, so it is the reciprocal of threads per inch. Imperial threads (UNC/UNF) are specified in TPI, while metric (M-series) threads are specified directly as pitch in millimeters.

pitch (mm) = 25.4 ÷ TPI

Understanding your result

Pitch and threads-per-inch are reciprocals, so a finer thread has a smaller pitch and more threads per inch. Use this to identify a fastener you cannot measure directly, but confirm the thread standard too, since metric and imperial threads of similar pitch are not interchangeable.

Example

20 TPI is a pitch of 0.05 inch, or 1.27 mm. A 1.5 mm metric pitch is about 16.93 TPI.

Sources & methodology

Last updated .

Frequently asked questions

How do TPI and pitch relate?

Pitch is the distance between threads, so it is the reciprocal of threads per inch: pitch (inch) = 1 ÷ TPI, and pitch (mm) = 25.4 ÷ TPI.

Which do imperial and metric threads use?

Imperial threads (UNC/UNF) are specified in threads per inch, while metric (M-series) threads are specified directly as pitch in millimeters.

Is my data stored?

No. Everything is calculated locally in your browser.