Thread Calculator

Construction

Calculate thread dimensions: pitch diameter, minor diameter, and thread depth for UN or metric threads.

Formula

UN: PD = major − 0.649519/TPI; minor = major − 1.299038/TPI; Metric: minor = major − 1.2269×pitch
  • UN threads: TPI = threads per inch. 1/2-13 UNC = 0.5 in major, 13 TPI.
  • Metric threads: input pitch in mm (e.g. M8×1.25 → major=8, pitch=1.25).
  • Thread depth: UN = 0.649519/TPI; Metric = 0.6134 × pitch.

1/2-13 UNC (0.5 in, 13 TPI)

Inputs
  • Thread Standard: UN
  • Major Diameter (UN: in; M: mm): 0.5
  • TPI (UN) or Pitch in mm (M): 13

Pitch = 1/13 = 0.07692 in. PD = 0.5 − 0.649519×0.07692 = 0.5 − 0.04996 = 0.45004 in.

Frequently asked questions

What is pitch diameter?
Pitch diameter is where the thread width equals the space between threads. For most purposes (nut-bolt fit), you want pitch diameter within class tolerance (1A/2A/3A for external, 1B/2B/3B for internal).