Nominal Size To OD Size Conversion Guide

Nominal Size 3/8"

Outside Diameter 1/2"

Fitting Needed 1/2" I.D.

Nominal Size 1/2"

Outside Diameter 5/8"

Fitting Needed 5/8" I.D.

Nominal Size 5/8"

Outside Diameter 3/4"

Fitting Needed 3/4" I.D.

Nominal Size 3/4"

Outside Diameter 7/8"

Fitting Needed 7/8" I.D.

Nominal Size      1"

Outside Diameter 1-1/8"

Fitting Needed 1-1/8" I.D.

Nominal Size 1- 1/4"

Outside Diameter 1-3/8"

Fitting Needed 1-3/8" I.D.

NOM. = Abrev. for Nominal

Common Terms (and what they mean)
  • C: A regular socket or hub. The pipe fits (sweats) inside this
  • FTG: The same size as the pipe. Will fit inside a socket /hub  fitting
  • Nominal: Used to describe copper pipe and fittings in plumbing terms. This refers to the inside diameter of the pipe and varies by the thickness of the pipe. The outside of a pipe is a constant size and is always 1/8" larger than the nominal size. Example: 1/2" nominal is always 5/8" O.D. or I.D in terms of HVAC sizes.