Pipe size converter
Convert a nominal pipe size between NPS and DN, or find the real outside diameter of a pipe, and back.
That's about the same as a 2" sprinkler main.
What it means
How big is that pipe?
Steel pipe to ASME B36.10 / ISO 6708. The outside diameter is the same for every schedule; the wall, and so the bore, changes. Copper tube and PVC have their own sizes.
Every unit
That pipe in every system
Learn
Three things worth knowing
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DN ≈ NPS × 25
NPS 1 = DN 25, NPS 2 = DN 50, NPS 4 = DN 100. A few break the pattern: NPS ½ is DN 15 and NPS 1¼ is DN 32.
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Iron pipe sizes
In the 1800s a 1-inch iron pipe had about a 1-inch bore. When stronger steel allowed thinner walls, the outside stayed put so threads and fittings still fitted.
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A ½" pipe is not ½"
NPS ½ measures 21.3 mm (0.84 in) outside. Buying fittings by measuring the pipe in inches gets the wrong size.
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Background
About nominal pipe sizes
A pipe’s name is not its size. NPS (nominal pipe size) began as the rough bore of early iron pipe; the outside diameter was then fixed so fittings would match, while walls got thinner. A 2-inch pipe is 60.3 mm (2.375 in) outside.
From NPS 14 up the name and outside diameter agree. Europe uses DN, a rounded millimeter label for the same pipe: NPS 2 is DN 50.