Thread Pitch & TPI Converter
Converts between thread pitch in millimetres and threads per inch across metric and imperial threads.
Enter Values
Minimum 0
How to use this calculator
- Enter either the thread pitch in mm (metric) or the threads per inch (imperial).
- Leave the other field blank.
- Read the converted value.
How it works
The Thread Pitch & TPI Converter switches between metric pitch and imperial threads-per-inch.
Pitch is the distance between adjacent threads. Since there are 25.4 mm per inch, pitch(mm) = 25.4 / TPI and TPI = 25.4 / pitch(mm).
Worked example
20 TPI. Pitch = 25.4 ÷ 20 = 1.27 mm per thread.
Frequently asked questions
Is pitch the same as lead?
For a single-start thread, yes. For multi-start threads the lead (advance per turn) is the pitch multiplied by the number of starts.
Does this identify a thread standard?
No — it only converts the pitch. Matching a thread also needs the diameter and form (e.g. metric M, UNC/UNF, BSP).
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Cite this tool
Zerdly. (2026). Thread Pitch & TPI Converter. Retrieved from https://www.zerdly.com/tools/thread-pitch-tpi-converter/
Length conversion table
How much one of each unit equals in the others — read each row as “1 [row unit] = …”. All values are exact conversions.
| 1 unit = | mm | cm | m | km | in | ft | yd | mi |
|---|---|---|---|---|---|---|---|---|
| 1 mm | 1 | 0.1 | 0.001 | 0.000001 | 0.03937 | 0.003281 | 0.001094 | 0.000001 |
| 1 cm | 10 | 1 | 0.01 | 0.00001 | 0.393701 | 0.032808 | 0.010936 | 0.000006 |
| 1 m | 1,000 | 100 | 1 | 0.001 | 39.370079 | 3.28084 | 1.093613 | 0.000621 |
| 1 km | 1,000,000 | 100,000 | 1,000 | 1 | 39,370.07874 | 3,280.839895 | 1,093.613298 | 0.621371 |
| 1 in | 25.4 | 2.54 | 0.0254 | 0.000025 | 1 | 0.083333 | 0.027778 | 0.000016 |
| 1 ft | 304.8 | 30.48 | 0.3048 | 0.000305 | 12 | 1 | 0.333333 | 0.000189 |
| 1 yd | 914.4 | 91.44 | 0.9144 | 0.000914 | 36 | 3 | 1 | 0.000568 |
| 1 mi | 1,609,344 | 160,934.4 | 1,609.344 | 1.609344 | 63,360 | 5,280 | 1,760 | 1 |
Tip: Enter any known values to calculate the remaining results.
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