Outside length: The length of the belt as measured around the outside.
Pitch length (PL): Imagine a belt traveling around a sheave, and you can see that the outside portion of the belt has to stretch and the inside portion has to compress as it goes around the curve of the sheave. The pitch length (PL) of a belt is the line somewhere in the belt that neither stretches nor compresses as it travels around the sheaves.
Nominal length: Nominal means the name given to something. The nominal length of a belt is simply the name given a certain size belt and is its approximate length. Nominal length is usually a bit less than pitch length. Most belts have the size and nominal length (such as A78) printed on the side.
Compare the nominal length, pitch length, and outside length of these belt sizes:
Adapted from HVAC Quick Tips by Leo Meyer; www.lamabooks.com.
Publication date: 02/21/2005