Pipe is generally identified by "Nominal Pipe Size" (NPS), with the wall thickness defined by "Schedule" (SCH). NPS is dimensionless designator and is an indication of a size but not an actual size. This is confusing for many people new to the piping industry. NPS 1/8 through NPS 12 has an outside diameter that is defined by the ansi pipe sizes. Generally speaking, a schedule 40 pipe dimension for up to 12 NPS is roughly equal to the ID of the pipe. Pipe sizes 14 and above are less confusing as a 14 NPS is equal to 14" OD (outer diameter).

Pipe Size Chart

ASME B 36.10 has more details of pipe sizes. The industry norm for pipe size also varies between different types of pipe. For a standard pipe, a 4.5" OD pipe will be referred to as 4" NPS however for line pipe and OCTG, it will be referred to as 4.5" only. Wall thickness is also mentioned differently. For standard pipe, pipe schedule is used to designate wall thickness. However line pipe is almost always referred by wall thickness whereas OCTG is referred by weight per foot.

Weight of Pipe

Weight of pipe is measured in pounds per foot or kilograms per meter. One should remember that weight of pipe in the ansi pipe size chart is "theoretical" weight and not an actual weight. Actual weight will vary based on the tolerance of pipe size.

Formula to calculate weight of steel pipe is;

W = [{OD-WT} x WT] x 10.69

W = Weight per lineal foot

OD = Outer Diameter

WT = Wall Thickness