Thread Pitch Calculator

Thread pitch is the distance between two adjacent thread crests on a screw or bolt — a measurement machinists, engineers, and DIYers need when matching fasteners or cutting threads. Select your thread system (Metric or Imperial), choose your calculation method, then enter your thread length, number of threads, TPI, or known pitch to get the thread pitch in mm, along with threads per inch, pitch in inches, and optionally the minor diameter if you supply a major diameter.

mm
mm
mm

Optional: for calculating minor diameter

Results

Thread Pitch

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Threads Per Inch (TPI)

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Pitch (inches)

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Minor Diameter

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Results Table

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Frequently Asked Questions

What is thread pitch?

Thread pitch is the distance between two adjacent threads on a threaded fastener. In metric threads, it's measured in millimeters, while in imperial threads, it's often expressed as threads per inch (TPI).

What is the thread pitch of a 2-inch long bolt that has a total of 48 threads?

To find the thread pitch: divide 2 inches by 48 threads = 0.04167 inches pitch. Converting to metric: 2 inches × 25.4 mm/inch = 50.8 mm, then 50.8 mm ÷ 48 threads = 1.058 mm pitch.

How do I measure thread pitch with a ruler?

Count the number of threads over a known length (like 1 inch or 25mm), then divide the length by the number of threads. For better accuracy, measure over a longer distance and use a magnifying glass.

What is metric thread pitch vs imperial TPI?

Metric thread pitch is the distance between threads in millimeters. Imperial TPI (threads per inch) is the number of threads in one inch. To convert: Pitch (mm) = 25.4 ÷ TPI.

What is a thread pitch gauge used for?

A thread pitch gauge is a precision tool with various thread profiles that you match against your fastener to determine the exact pitch. It's more accurate than measuring with a ruler and commonly used by machinists.

How do I figure out thread pitch without measuring?

If you know the thread designation (like M8×1.25 or 1/4-20), the pitch is included in the specification. M8×1.25 means 8mm diameter with 1.25mm pitch, while 1/4-20 means 20 TPI.

What's the difference between UNC and UNF threads?

UNC (Unified National Coarse) threads have fewer threads per inch for faster assembly, while UNF (Unified National Fine) threads have more threads per inch for greater holding strength and finer adjustment.

Can I convert between metric and imperial thread pitch?

Yes, but they're not directly interchangeable due to different thread profiles. You can convert the pitch measurements: Imperial pitch (inches) = Metric pitch (mm) ÷ 25.4, and TPI = 25.4 ÷ Metric pitch (mm).