Nominal pipe size refers to only the outside diameter (OD) of a pipe making it somewhat vague. For example, when we say pipe size is 2 NPS, it refers to all the pipes having 2.375-inch (or 60.3 mm) as outside diameter irrespective of wall thickness and thus the inside diameter.

What does nominal size mean for pipe?

Nominal Pipe Size (NPS) is a North American set of standards used to designate pipe diameter and thickness. Pipe size is specified with two non-dimensional numbers: a nominal pipe size (NPS) for inside diameter based on inches, and a schedule (Sched. or Sch.) for wall thickness.

What is the unit of nominal pipe size?

Nominal pipe size (NPS) is a dimensionless designator of pipe size. It indicates standard pipe size when followed by the specific size designation number without an inch symbol. For example, NPS 6 indicates a pipe whose outside diameter is 168.3 mm.