Standard pipe sizes

Updated April 17, 2017

Pipes and pipe-fitting may not be exciting, but there is plenty of excitement if pipes fail. Standards for pipe sizes help you find a pipe that fits, but they also ensure your comfort and safety. It's important to make sure they are the right size.


In 1927, the American Standards Association adopted the Nominal Pipe Size (NPS), a North American pipe size standard. The American Standards Association has since been changed to the American National Standards Institute (ANSI), and the standard has been periodically updated to reflect new materials and uses.


Standard pipe sizes are measured by the diameter of the outside of the pipe. The thickness of the pipe's wall itself is associated with pressure load, which can be determined from the pipe's "schedule," a list of the engineering specifications for each type and size of pipe.


Standard pipe sizes are designated in two different systems, North American and European. The European system is called Nominal Diameter (DN) and is measured in millimetres. The North American system is called Nominal Bore (NB) and is measured in inches.

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About the Author

Stanley Goff began writing in 1995. He has published four books: "Hideous Dream," "Full Spectrum Disorder," "Sex & War" and "Energy War," as well as articles, commentary and monographs online. Goff has a Bachelor of Arts in English from the University of the State of New York.