Conversion History
TPI to MM Converter
Convert TPI to MM quickly with this simple online calculator. Enter a Threads Per Inch value to find the equivalent thread pitch in millimeters. You can also enter the pitch in millimeters to calculate the corresponding TPI.
What Is TPI
TPI stands for Threads Per Inch. It tells you how many threads are present in one inch of a threaded component. TPI is commonly used when working with inch-based screws, bolts, nuts, pipes, and other threaded parts.
For example, a specification of 20 TPI means that there are 20 threads in one inch. The TPI value can then be converted into millimeters to find the distance between two adjacent threads.
What Is Thread Pitch in MM
Thread pitch is the distance from one thread to the next. When the pitch is expressed in millimeters, it is normally written as a value such as 1.27 mm, 2.54 mm, or 0.635 mm.
TPI and metric thread pitch use different ways to describe thread spacing. Converting between them is useful when comparing inch-based and metric thread specifications.
TPI to MM Formula
The TPI to MM conversion uses a straightforward formula:
One inch is equal to 25.4 millimeters. Therefore, dividing 25.4 by the TPI value gives the distance between the threads in millimeters.
How to Convert TPI to MM
- Take the TPI value you want to convert.
- Divide 25.4 by the TPI value.
- The answer is the thread pitch in millimeters.
25.4 ÷ 20 = 1.27 mm
Therefore, 20 TPI = 1.27 mm.
Common TPI to MM Conversions
| TPI | Thread Pitch (MM) |
|---|---|
| 4 | 6.3500 mm |
| 5 | 5.0800 mm |
| 6 | 4.2333 mm |
| 8 | 3.1750 mm |
| 10 | 2.5400 mm |
| 12 | 2.1167 mm |
| 14 | 1.8143 mm |
| 16 | 1.5875 mm |
| 18 | 1.4111 mm |
| 20 | 1.2700 mm |
| 24 | 1.0583 mm |
| 28 | 0.9071 mm |
| 32 | 0.7938 mm |
| 36 | 0.7056 mm |
| 40 | 0.6350 mm |
| 48 | 0.5292 mm |
| 56 | 0.4536 mm |
| 64 | 0.3969 mm |
Examples of TPI to MM Conversion
For 10 TPI, divide 25.4 by 10:
For 32 TPI:
For 40 TPI:
TPI and Thread Pitch: What Is the Difference
TPI and thread pitch describe thread spacing using different units. TPI tells you the number of threads per inch, while thread pitch tells you the distance between adjacent threads.
Because one inch is 25.4 mm, the two measurements can be converted using a simple mathematical relationship.
A higher TPI value means the threads are closer together, so the resulting pitch in millimeters becomes smaller.
Why Convert TPI to MM
TPI to MM conversion can be useful when working with different thread measurement systems. It can help when comparing threaded components, checking specifications, reading engineering information, or working with both inch and metric measurements.
- Comparing inch and metric thread specifications
- Checking screw and bolt thread spacing
- Working with threaded components
- Reading engineering measurements
- Checking thread pitch during machining
- Comparing different thread standards
How to Use This TPI to MM Converter
Enter the TPI value in the first box. The calculator will automatically calculate the equivalent pitch in millimeters.
You can also enter a value in the MM field to calculate the corresponding TPI. The swap button lets you switch the two fields, while the quick-select buttons provide commonly used TPI values.
If you want to keep a conversion for later reference, use the Save History button. The calculator stores the recent conversions in your browser. You can also download a PDF report of the current conversion and saved history.
Frequently Asked Questions
TPI stands for Threads Per Inch. It represents the number of threads found within one inch of a threaded component.
Divide 25.4 by the TPI value. The formula is MM = 25.4 ÷ TPI. For example, 20 TPI is 1.27 mm.
20 TPI is equal to 1.27 mm thread pitch.
10 TPI is equal to 2.54 mm thread pitch.
40 TPI is equal to 0.635 mm thread pitch.
No. TPI tells you the number of threads per inch, while thread pitch is the distance between adjacent threads. TPI can be converted to thread pitch in millimeters using 25.4 ÷ TPI.
Yes. Since the pitch is calculated by dividing 25.4 by TPI, a higher TPI value produces a smaller thread pitch.
Yes. To convert millimeter thread pitch back to TPI, divide 25.4 by the pitch in millimeters. This calculator supports both directions.
Final Thoughts
TPI to MM conversion is useful whenever you need to compare inch-based thread measurements with metric thread pitch. The calculation is simple: divide 25.4 by the TPI value.
Use the calculator above for quick two-way conversion, common TPI values, saved conversion history, and PDF output without doing the calculation manually.