Tips and Notes

Nominal Pipe Size (NPS)

Nominal Pipe Size (NPS) is a North American set of standard sizes for pipes used for high or low pressures and temperatures.

Where applicable, this website uses NPS (Nominal Pipe Size) instead of INCH for the OUTER DIAMETER (OD) of pipes, flanges, fittings, etc., and that is the only correct way to describe the outer dimensions.

The Germans, for example, have a similar system, with a dimensionless designator, in which the outer diameter is described using DN (Diameter Nominal).