How this calculator works
Pitch is the axial distance between matching points on neighbouring threads. TPI is the reciprocal spacing in inches. Count spaces between crests rather than the crests themselves: eleven crests span ten intervals. Multiple-start thread lead is a different quantity.
Formula
pitch = measured length / intervals; TPI = 0.0254 / pitch in metres; measured length = pitch x intervals.
Worked example
A 12.7 mm length across ten thread intervals gives 1.27 mm pitch and 20 TPI. A 1.5 mm pitch gives 16.9333 TPI.
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Frequently asked questions
Can I count crests instead of intervals?
Subtract one from the crest count when measuring from the first crest to the last.
Does pitch identify the complete thread?
No. Major diameter, profile, handedness and tolerance class also matter.
Is lead equal to pitch?
Only for a single-start thread. Lead equals pitch times the number of starts.