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Thread Pitch Calculator
Pick whether you’re starting from imperial threads-per-inch or a metric pitch in millimeters, enter the value, and get the equivalent in both systems.
What This Calculator Does
Screw threads are specified either by threads per inch (TPI) in imperial systems or by pitch in millimeters in metric systems. This calculator converts a value from either system into the other so you can match or identify a fastener’s thread.
The Formula
Pitch is simply the distance from one thread crest to the next. In imperial threads, pitch (inches) equals 1 divided by TPI. To convert to metric, multiply the pitch in inches by 25.4 to get millimeters. Going the other way, divide a metric pitch in millimeters by 25.4 to get pitch in inches, then take its reciprocal to get TPI.
Good to Know
- Metric and imperial threads with similar numbers are rarely truly interchangeable — always confirm both pitch and major diameter match before mating parts.
- This is a mathematical conversion for reference and planning; verify critical fastener compatibility with a thread gauge.
Last reviewed August 2026