MasterTool

Thread Pitch Calculator

Convert between threads per inch and metric thread pitch in both directions.

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What this tool does

Convert between threads per inch and metric thread pitch in both directions. Pitch is the distance between adjacent thread crests. Imperial threads are specified by TPI (e.g. 1/4-20), metric by pitch in mm (e.g. M6 × 1.0).

How to use the Thread Pitch Calculator

  1. Enter or select i know the.
  2. Enter or select threads per inch.
  3. Enter or select metric pitch (mm).
  4. Read the calculated result; change any measurement to compare alternatives.

Formula

pitch (in) = 1 / TPI; pitch (mm) = 25.4 / TPI; TPI = 25.4 / pitch (mm)
basis
I know the
tpi
Threads per inch
pitchMm
Metric pitch (mm)

Pitch is the distance between adjacent thread crests. Imperial threads are specified by TPI (e.g. 1/4-20), metric by pitch in mm (e.g. M6 × 1.0).

Worked example

For thread pitch calculator, the following measurements illustrate the exact method: I know the: tpi; Threads per inch: 20; Metric pitch (mm): 1.25.

Inputs

  • I know theThreads per inch (TPI)
  • Threads per inch20
  • Metric pitch (mm)1.25

Result

  • Thread pitch1.27 mm
  • Thread pitch (in)0.05 in
  • Threads per inch20

Results explained

Thread pitch
Thread pitch from the formula above. Pitch is the distance between adjacent thread crests. Imperial threads are specified by TPI (e.g. 1/4-20), metric by pitch in mm (e.g. M6 × 1.0).
Thread pitch (in)
Thread pitch (in) from the formula above. Pitch is the distance between adjacent thread crests. Imperial threads are specified by TPI (e.g. 1/4-20), metric by pitch in mm (e.g. M6 × 1.0).
Threads per inch
Threads per inch from the formula above. Pitch is the distance between adjacent thread crests. Imperial threads are specified by TPI (e.g. 1/4-20), metric by pitch in mm (e.g. M6 × 1.0).

Frequently asked questions

Pitch in mm = 25.4 ÷ TPI. A 20 TPI thread has a pitch of 1.27 mm; a 13 TPI thread (¼ in pipe/coarse bolts) is about 1.95 mm.

1.0 mm by definition — metric callouts print the pitch after the ×. Its TPI equivalent is 25.4, which is why M6 × 1.0 and 1/4-20 hardware feel similar but never interchange.

Count crests over a known length for TPI (or use a thread pitch gauge: the leaf that seats with no light gap is the pitch). Measure several threads and divide to average out error.

For M8, 1.25 mm is the standard coarse pitch (fine is 1.0). 'Coarse' and 'fine' are defined per diameter in the ISO/ASME tables — pitch alone does not say.

Close is not compatible: 1/4-20 (1.27 mm pitch, 60° UNC form, inch diameter) vs M6 × 1.0 differ in both diameter and pitch, and forcing them damages both parts.