Thread Pitch Calculator
Calculate thread pitch accurately for your build. Get material quantities, waste allowances, and project cost breakdowns.
Reviewed by Abdullah, Technical Content Specialist
Formula
Pitch = Measurement Length / Thread Count | TPI = 25.4 / Pitch(mm)
Thread pitch is determined by dividing the measured distance by the number of threads counted in that span. To convert between metric pitch (mm) and imperial TPI, use: TPI = 25.4 / Pitch and Pitch = 25.4 / TPI. Thread geometry values derive from the 60-degree ISO thread profile: Height = 0.866 x Pitch, Depth = 0.6134 x Pitch.
Worked Examples
Example 1: Measuring Unknown Thread Pitch
Problem:You count 10 complete threads over a span of 15mm. What is the thread pitch and equivalent TPI?
Solution:Pitch = Distance / Thread Count = 15 / 10 = 1.5 mm\nTPI = 25.4 / 1.5 = 16.93\nThread Height = 0.866 x 1.5 = 1.299 mm
Result:Pitch = 1.5 mm (16.93 TPI) - This is a standard M-series coarse pitch
Example 2: Converting 20 TPI to Metric
Problem:Convert a 20 TPI imperial thread to metric pitch.
Solution:Pitch = 25.4 / TPI = 25.4 / 20 = 1.270 mm\nThread Height = 0.866 x 1.27 = 1.100 mm
Result:Pitch = 1.270 mm
Frequently Asked Questions
How do I measure thread pitch?
The simplest method is to count a known number of thread crests over a measured distance and divide the distance by the number of threads. For example, if 10 threads span 15mm, the pitch is 1.5mm. A thread pitch gauge (a set of thin blades with tooth profiles) provides the most reliable identification by matching the blade to the thread. For imperial threads, count the threads in one inch to get the TPI (threads per inch) value directly.
What is the difference between thread pitch and threads per inch?
Thread pitch is the distance from one thread crest to the next adjacent crest, measured in millimeters for metric threads. Threads per inch (TPI) is the number of thread crests in one inch of length, used for imperial/unified threads. They are inversely related: TPI = 25.4 / Pitch(mm) and Pitch(mm) = 25.4 / TPI. Metric threads use pitch (e.g., M10 x 1.5 means 1.5mm pitch) while unified threads use TPI (e.g., 1/2-13 means 13 TPI).
How do I convert between metric pitch and TPI?
To convert metric pitch to TPI, divide 25.4 by the pitch in millimeters. For example, 1.5mm pitch = 25.4 / 1.5 = 16.93 TPI. To convert TPI to metric pitch, divide 25.4 by the TPI. For example, 13 TPI = 25.4 / 13 = 1.954mm pitch. Note that metric and imperial threads are not interchangeable even if the numbers are close, as the thread form profiles differ slightly and tolerances are specified differently.
What are common metric thread pitches?
Standard coarse metric thread pitches increase with diameter: M3 uses 0.5mm, M4 uses 0.7mm, M5 uses 0.8mm, M6 uses 1.0mm, M8 uses 1.25mm, M10 uses 1.5mm, M12 uses 1.75mm, M16 uses 2.0mm, M20 uses 2.5mm, and M24 uses 3.0mm. Fine pitch variants are also available for each size, typically 60-75% of the coarse pitch value. Fine pitch is specified with both values, e.g., M10 x 1.25 for fine versus M10 x 1.5 for coarse.
References
Reviewed by Abdullah, Technical Content Specialist · Editorial policy