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Calculate threads per inch (TPI) from thread count, length, or pitch. Convert thread pitch between inches and mm with our free TPI calculator.
Need to know the thread size of a screw or bolt? Our threads per inch calculator makes it easy. It helps you find TPI from thread count and length. You can also use thread pitch to find TPI.
We developed this calculator so users can find thread sizes with ease. It works with both inch and metric units. You can also convert TPI into thread pitch in inches and millimeters.
This tool can help with bolts, screws, nuts, and threaded rods. It's useful for DIY jobs, machine work, and fastener checks.
Threads per inch (TPI) means the number of thread gaps in one inch. It shows how close the threads sit on a bolt or screw.
A high TPI means the threads sit close together. A low TPI means they sit farther apart.
Think of a staircase. More steps in the same space mean less room between each step. TPI works in much the same way.
You can find TPI in three ways.
1. From thread count and length:
TPI = Number of Thread Intervals ÷ Length in Inches
2. From thread pitch in inches:
TPI = 1 ÷ Thread Pitch (inches)
3. From thread pitch in millimeters:
TPI = 25.4 ÷ Thread Pitch (mm)
Reverse thread pitch formulas:
Pitch (inches) = 1 ÷ TPI
Pitch (mm) = 25.4 ÷ TPI
Here, 25.4 is the number of millimeters in one inch.
Our TPI calculator has three easy modes.
Choose a mode: Select Count / Length, Thread Pitch, or Reverse.
Enter thread count: For the first mode, enter the thread intervals and length.
Select a unit: Choose inches or millimeters as needed.
Enter your value: For pitch mode, enter the thread pitch. For reverse mode, enter TPI.
Calculate: Submit your values to see the result and calculation details.
The tool checks your inputs before it shows a result. All values must be valid and above zero.
Let's find TPI from thread count and length.
Suppose a bolt has 20 thread intervals across one inch.
Given:
Number of thread intervals = 20
Measured length = 1 inch
Formula:
TPI = Number of Thread Intervals ÷ Length
Calculation:
TPI = 20 ÷ 1
Answer: 20 TPI
This means the bolt has 20 thread intervals per inch.
You can also find TPI from metric pitch. For example, a pitch of 1.25 mm gives:
TPI = 25.4 ÷ 1.25
TPI = 20.32
TPI helps you find the right bolt, screw, or nut. A wrong thread size can cause poor fit or damage.
It also helps you:
Match bolts with nuts.
Check screw thread size.
Compare metric and inch threads.
Choose the right fastener.
Check threaded rods for repair work.
Always check the thread type and diameter too. TPI alone cannot confirm a perfect fit.
Our threads per inch calculator helps you find TPI fast. It supports thread count, length, and pitch inputs. It also converts TPI into inch and metric pitch.
Whether you're fixing a bolt or checking a screw, this tool saves time. Enter your values and get your result with ease.
TPI means threads per inch. It tells you how many thread intervals fit within one inch.
Divide the number of thread intervals by the measured length in inches.
Divide 1 by pitch in inches. For metric pitch, divide 25.4 by pitch in millimeters.
A 20 TPI thread has a pitch of 1.27 mm.
No. TPI counts thread intervals per inch. Pitch measures the gap between two nearby thread peaks.
Yes. This calculator accepts millimeters for length and thread pitch. It converts the values as needed.