BoltLabThread Pitch to TPI Converter
Quick answer
Thread pitch in millimeters is the axial distance per thread; TPI counts threads per inch.
Drawings may show either unit, so conversions prevent mismatched taps and gages.
Use the converter below, then read thread types when you separate UNC from metric coarse.
Switch mode and type your value. Result updates immediately with no submit button.
Use thread types for naming when drawings mix series labels.
Use the thread identifier when matching unknown parts.
Converter
Formula used
TPI = 25.4 / pitch(mm) and pitch(mm) = 25.4 / TPI.
FAQ
How do you convert thread pitch to TPI?
Divide 25.4 by the metric pitch value in millimeters. Example: 25.4 / 1.25 = 20.32 TPI.
Can I convert TPI back to metric pitch?
Yes. Enter a TPI value and the calculator computes pitch in millimeters instantly using pitch = 25.4 / TPI.
Engineering references
Pitch conversion is one step in fit analysis. Continue with Thread Engineering Reference, tolerance zones, and ISO tolerances to complete the engineering workflow.