Measuring fitting sizes

Nominal pipe size refers to the inner diameter of a pipe. Pipe fitting size refers to the pipe size that the fitting fits to. For example a 1/2″ pipe, the inner diameter of the pipe would be 1/2″. Outer diameter would depends on the wall thickness. To find the correct fitting size, measure the outer diameter of the threads.

  • For a male thread, measure¬†the outer diameter ¬†(OD) of the thread.
  • For a female thread, measure the top diameter of the opening (OD).

Measure the outer diameter of the thread, then look up the table below for the next nearest nominal pipe size.

OD (inches) Nominal Pipe Size (inches)
0.405 1/8
0.540 1/4
0.675 3/8
0.840 1/2
1.050 3/4
1.315 1
1.660 1-1/4
1.900 1-1/2
2.374 3