Thread Count Converter
Convert between threads per inch (TPI), metric thread pitch in mm, and standard thread sizes.
Type in any field — the others update instantly.
Thread pitch and TPI measure the same thing — how close threads are spaced.
TPI (Threads Per Inch): Number of threads in one inch. Used in imperial/US systems (UNC, UNF).
Pitch (mm): Distance between thread crests in millimeters. Used in metric systems (ISO metric threads).
Conversion formula:
- Pitch (mm) = 25.4 / TPI
- TPI = 25.4 / Pitch (mm)
Common thread standards:
| Thread | TPI | Pitch (mm) |
|---|---|---|
| 1/4"-20 UNC | 20 | 1.270 |
| 1/4"-28 UNF | 28 | 0.907 |
| 5/16"-18 UNC | 18 | 1.411 |
| 3/8"-16 UNC | 16 | 1.588 |
| 1/2"-13 UNC | 13 | 1.954 |
| M3 × 0.5 | 50.8 | 0.500 |
| M4 × 0.7 | 36.3 | 0.700 |
| M5 × 0.8 | 31.8 | 0.800 |
| M6 × 1.0 | 25.4 | 1.000 |
| M8 × 1.25 | 20.3 | 1.250 |
| M10 × 1.5 | 16.9 | 1.500 |
| M12 × 1.75 | 14.5 | 1.750 |
UNC = Unified National Coarse. UNF = Unified National Fine.