Formula: 25.4 ÷ 1.0 mm = 25.4 threads per inch.
Metric Thread Pitch to TPI Converter
Convert millimeter thread pitch to threads per inch, or convert TPI back to metric pitch. Use it when comparing metric fasteners, inch taps, thread gauges, lathe settings, and repair notes.
Convert thread pitch
Enter either metric pitch or TPI. The converter updates the other value and shows nearby common thread pitches.
Closest metric pitchM6 × 1.0 style pitch
Closest inch TPI26 TPI / 24 TPI nearby
Pitch spacing0.0394 in per thread
A 1.0 mm metric pitch equals 25.4 threads per inch. It sits between 24 TPI and 26 TPI, so do not treat either as an exact replacement.
How to use this converter
- Choose metric pitch or TPI as your starting value.
- Enter the pitch shown on your thread gauge, drawing, tap, die, or fastener callout.
- Read the converted pitch and compare the nearby common options.
- Confirm diameter and thread standard before cutting, chasing, or replacing a thread.
Thread pitch formulas
Metric pitch to TPI: TPI = 25.4 ÷ pitch in mm.
TPI to metric pitch: pitch in mm = 25.4 ÷ TPI.
The number 25.4 is the exact number of millimeters in one inch.
Common metric pitch and TPI equivalents
Quick reference for common metric pitches and inch thread counts. Nearby values are useful for identification, not automatic interchange.
| Starting pitch | Converted pitch | Common use | Note |
|---|
Metric pitch and TPI FAQ
Is 1.25 mm the same as 20 TPI?
Not exactly. A 1.25 mm pitch is about 20.32 TPI. A 20 TPI thread has a 1.27 mm pitch. They are close enough to confuse during measuring, but not the same thread specification.
What TPI is M6 × 1.0?
M6 × 1.0 has a 1.0 mm pitch, which converts to 25.4 TPI. The M6 part is the nominal diameter; the 1.0 part is the pitch.
Why do metric threads use pitch instead of TPI?
Metric thread callouts list the distance from one thread crest to the next in millimeters. Inch thread callouts usually list how many thread peaks fit in one inch.