ABSTRACT
Pipe is sized by its inside diameter or ID. The wall thickness varies in proportion to the diameter according to the nominal pipe size, or NPS, but is generally between 1 8 ″ and 316 ″, so 1-inch pipe is actually almost 1516 ″
on the outside. Other types of structural steel such as square or round tubing are sized by their outside diameter or OD. Of course, it is much easier to make up a cut list if you are given the exterior dimensions of the materials.
