For example, if the circumference is 12. 57 inches (319 mm), you would divide by pi, and get an outside diameter of about 4 inches (100 mm). Use string to measure if you don’t have measuring tape. Mark the point on the string where it wraps around the circumference. Then remove the string, measure it against a ruler, and divide that length by pi.
Remember not to measure from the outside edges, but rather from inside edge to inside edge.
If you are unsure, it could help to go to the website of a store in your country that sells pipe. If they mark pipe with inches, then you need the NPS system.
This table is helpful for NPS measurements: https://www. zoro. com/pipe-fitting-size-guide This table has both NPS and DN measurements: https://www. massflow-online. com/faqs/where-do-nps-or-dn-stand-for/ For example, if you measured a diameter of 1. 05 inches (27 mm), this would translate to a nominal size of ¾ in NPS, or 20 in DN.
