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Threads

Thread Pitch and TPI Converter

Convert the spacing of a thread between metric pitch and threads per inch. The numeric conversion is exact, but the result may not correspond to a standard thread series.

LOCAL CALC / THREAD-PITCH
NO DATA SENT

INPUT

Enter values

Enter mm pitch in the first mode, TPI in the second.

OUTPUT

READY

Enter known values and calculate.

Results stay on this device.
Shop-floor check

Never identify or mate a thread from pitch alone. Confirm diameter, form, angle, class, handedness, taper, and the governing standard.

01 / METHOD

How to use this calculator

  1. Choose the direction of conversion.
  2. Enter a positive pitch or TPI value.
  3. Calculate and compare with the relevant thread chart.

02 / APPLICATION

Where it helps

  • Interpreting mixed-unit drawings
  • Comparing lead screw or thread spacing
  • Identifying a close nominal thread series

03 / BOUNDARIES

Assumptions and limitations

Assumes

  • Single-start thread when interpreting pitch as lead
  • Exactly 25.4 millimetres per inch
  • Input represents thread spacing, not diameter

Does not cover

  • Does not identify thread form or class
  • A close result is not proof of thread identity
  • Multi-start thread lead differs from pitch

04 / QUESTIONS

Frequently asked questions

Does 1.5 mm equal a standard inch thread?

It converts to about 16.933 TPI, which is not the same as a 16 or 18 TPI standard thread.

Are pitch and lead the same?

They are the same for a single-start thread. On a multi-start thread, lead equals pitch multiplied by the number of starts.

Can this identify an unknown thread?

It can help, but pitch alone is insufficient. Measure diameter and inspect form, taper, and angle against a standard.