Thread Pitch Converter
Convert screw thread pitch between millimetres and threads per inch (TPI) — for matching bolts, nuts and taps in the workshop. Enter a value in either unit and get the exact conversion instantly.
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How to use
- Enter the thread pitch in millimetres, for example 1.25.
- The matching value in threads per inch (TPI) appears at once.
- Enter a TPI value instead to convert back to millimetres.
- Check a reading by hand with TPI = 25.4 ÷ pitch in mm.
Good to know
- Common coarse pitches: M6×1.0, M8×1.25, M10×1.5, M12×1.75 — useful for quick identification.
- TPI = 25.4 ÷ pitch(mm), so a 1.25 mm pitch equals about 20.3 TPI.
- Bolt identity needs both diameter and pitch — pitch alone is not enough.
Note
TPI = 25.4 / pitch (mm). Common metric coarse pitches: M6 = 1.0 mm, M8 = 1.25 mm, M10 = 1.5 mm, M12 = 1.75 mm. Bolt size is made from diameter and pitch together.