Thread Pitch Calculator
Thread pitch is the axial distance from one thread crest to the next. Metric threads name pitch in millimetres; inch threads usually use threads per inch, so pitch and TPI are two ways to describe the same spacing.
thread pitch thread pitch calculator thread pitch chart tpi calculator
Pitch and TPI conversion
For Unified inch-series threads, pitch in inches is one divided by TPI. To compare against metric pitch, convert inches to millimetres.
pitch_mm = 25.4 / TPI
Where pitch is used
- Tap drilling: pitch and percent engagement set the tap drill diameter.
- Rigid tapping: feed per revolution equals thread pitch.
- Three-wire measurement: pitch and wire diameter define the pitch-diameter correction.
Chart-first lookup
If you know the designation, such as M8 x 1.25 or 1/4-20 UNC, the thread pitch chart is faster than measuring or back-solving.
Frequently asked questions
How do I calculate pitch from TPI?
Use pitch_mm = 25.4 / TPI. For 20 TPI, pitch is 25.4 / 20 = 1.27 mm.
Is thread pitch the same as thread pitch diameter?
No. Pitch is thread spacing. Pitch diameter is a diameter through the thread profile, often checked with the three-wire method.
Related pages
- Thread pitch chart - metric coarse/fine and Unified UNC/UNF pitch and TPI reference.
- Thread pitch diameter calculator - three-wire pitch-diameter measurement workflow.
- Thread identifier - workbench for narrowing thread size from measured diameter and pitch.
- Tap drill size calculator - tap drill diameter from thread size and percent engagement.
- Tapping feed-rate calculator - feed rate from spindle RPM and thread pitch.