All charts / Machining
Pipe Size Chart (Schedule 40)
Nominal pipe size with outside diameter and Schedule 40 wall thickness in millimetres.
| NPS | Outside dia. (mm) | Wall, Sch 40 (mm) | Inside dia. (mm) |
|---|
Standard: ASME B36.10 · Data checked: 2026-10-14
Frequently asked questions
What is the difference between nominal size and actual outside diameter?
Nominal pipe size is a label, not a measurement. A 2 inch pipe has an outside diameter of 2.375 in, not 2 in. The outside diameter was fixed so that fittings and threads would interchange, and the wall thickness — and therefore the inside diameter — changes with the schedule.
What does Schedule 40 mean?
It is a wall thickness series. For a given nominal size, a higher schedule number means a thicker wall and a smaller bore. Schedule 40 is the common general-purpose series; Schedule 80 is thicker and used for higher pressure and for threaded connections, which need the extra wall to cut the thread into.
How do I work out the inside diameter?
Outside diameter minus twice the wall thickness. The pipe table lists outside diameter and wall thickness for Schedule 40, from which the bore follows. Do not assume the bore equals the nominal size — for small sizes it can be considerably smaller.
Can I use the outside diameter to size a fitting?
For a given nominal size and standard, yes — the outside diameter is what fittings match. That is the whole reason the outside diameter was standardised while the bore was allowed to vary.