Steel pipe measurements

　　Before we can read a pipe sizing chart, we need to understand what different measurements or dimensions are being listed.

　　Length: This is fairly self-explanatory — it designates how long a piece of piping is, usually in standard increments.

　　Inside diameter (ID): The inside diameter is the distance between the inside walls. It can be thought of as how wide the opening in the pipe is.

　　Outside diameter (OD): The outside diameter is the distance from the outside edge to its opposite outside edge. This can be thought of as the total “height” of the pipe.

　　Wall thickness (WT): Similar to length, this is relatively self-explanatory and is the thickness of the piping’s wall. It is also half of the difference between OD and ID. Wall thickness is usually referred to as “schedule” which is a non-dimensional number that needs to be converted to the actual wall thickness using a chart.

　　Nominal pipe size (NPS): This is the metric that is most often used to convey the “size” of a pipe. However, the NPS is neither the ID nor the OD when it’s between ?” and 12”. This means that, while close to the actual diameter of the pipe, it’s another non-dimensional number and more of a designation rather than a measurement. Above 14” (or NPS 14), the nominal pipe size and OD are the same.