Standard sizes for HDPE pipes are between three-quarters of inch all the way up to 63 inches in increments of one or more inches. HDPE pipes are measured according to their nominal size, which is the distance from one of the pipe's inner walls to the other.
While nominal size is the most important measurement for HDPE pipes, several other values are also relevant. The pipe's outer diameter is the distance from a point on the outside of the pipe's wall to a point on the opposite outer wall. Wall thickness is also an important value, as it relates to how much internal pressure the pipe can withstand. Most manufacturers produce HDPE pipes in a range of different wall thicknesses for pipes with different service applications.
A pipe that carries pressurized water, for instance, requires walls thick enough to prevent ruptures. An HDPE pipe used to carry storm water or sewage, on the other hand, only requires very thin walls as these pipes almost never experience even moderate pressures. HDPE stands for high density polyethylene, a type of very durable plastic. Aside from pipes, HDPE is used in the manufacture of bottles and bottle caps, cable coatings and some types of engineered wood. HDPE is a good choice for storing and transporting liquids as, unlike many other types of plastic, it does not contaminate fluids with the harmful chemical bisphenol A.