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Thread Spacing & TPI Calculator

Relate thread pitch, measured length and threads per inch.

  • Formula & worked example
  • Private in your browser
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Calculator inputs

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Edit a calculated value to solve backwards, or lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

Private by default

Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.

Formula and method

Divide the measured axial length by the number of thread intervals. Twenty intervals across one inch give a pitch of 0.05 inch and 20 threads per inch.

Pitch = axial length ÷ thread intervals; TPI = 1 ÷ pitch in inches

Worked example

Enter these known values and leave the other values blank.

Thread length (L)
1 in
Total number of threads (n)
20 threads
Threads per inch (TPI)
20
Thread pitch (P)
0.05 in

Assumptions and limitations

  • Count complete intervals across the measured length. If both end crests are included, the number of intervals is one fewer than the number of crests. Pitch alone does not identify thread angle, diameter or standard.
  • Use the units shown beside each field. This model assumes the stated relationship and does not account for quantities left out of the formula.

Common questions

Should I count crests or gaps?

Count complete intervals across the measured length. If both end crests are included, the number of intervals is one fewer than the number of crests. Pitch alone does not identify thread angle, diameter or standard.

References

The calculation equations, inverse formulas, units, and input rules were imported from this source. Bookify provides the interface and equation solver.

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