Convert metric or inch thread pitch to TPI and back, then see lead per revolution, thread count over a measured length, and a common-TPI comparison.
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Pitch To TPI Formula
The following equation is used to calculate the pitch from the threads per inch.
- Where Pitch is the thread pitch in millimeters (mm)
- TPI is the threads per inch
For pitch in millimeters, TPI = 25.4 ÷ pitch and pitch = 25.4 ÷ TPI. For pitch in inches, TPI = 1 ÷ pitch. Lead per revolution equals pitch multiplied by the number of thread starts; thread starts do not change TPI.
| Pitch (mm) | Threads Per Inch (TPI) |
|---|---|
| 0.25 | 101.600 |
| 0.3 | 84.667 |
| 0.35 | 72.571 |
| 0.4 | 63.500 |
| 0.5 | 50.800 |
| 0.6 | 42.333 |
| 0.7 | 36.286 |
| 0.75 | 33.867 |
| 0.8 | 31.750 |
| 1 | 25.400 |
| 1.25 | 20.320 |
| 1.5 | 16.933 |
| 1.75 | 14.514 |
| 2 | 12.700 |
| 2.5 | 10.160 |
| 3 | 8.467 |
| 3.5 | 7.257 |
| 4 | 6.350 |
| 5 | 5.080 |
| 6 | 4.233 |
| Formula: TPI = 25.4 ÷ pitch(mm). Conversion factor: 1 inch = 25.4 mm. | |
What Does “Pitch to TPI” Mean?
Definition:
The Pitch to TPI conversion translates axial thread pitch in millimeters into threads per inch using exactly 25.4 millimeters per inch. Matching the resulting pitch alone does not establish compatibility: diameter, thread form, handedness, starts and tolerances must also match.
How to Calculate Pitch To TPI?
Example Problem:
The following example outlines the steps and information needed to determine the pitch when the threads per inch are provided.
First, determine the threads per inch. In this example, the threads per inch is 8.
Next, calculate the pitch using the formula above.
Pitch = 25.4 / TPI
Pitch = 25.4 / 8
Pitch = 3.175 mm
FAQ
What does the pitch to TPI conversion represent?
The conversion expresses the same axial thread spacing as pitch in millimeters or threads per inch. It does not identify a compatible metric or imperial thread standard by itself.
Why is the conversion factor 25.4 used in this calculator?
The value 25.4 is used because it is the exact number of millimeters in one inch, allowing for precise conversion between millimeters and inches.
When should I use the Pitch To TPI calculator?
You should use this calculator when you have one measurement (either pitch in mm or threads per inch) and you need to accurately determine the other, particularly when working with components that use different measurement systems.
