Why 24 inch pipe is not 24 inches
Nominal Pipe Size is a label, not a measurement. NPS 24 pipe has an outside diameter of 24.000 inches, and it keeps that outside diameter in every schedule made. What the schedule number changes is the wall: at schedule 5s the wall is 0.218 inches, so the bore comes out at 23.564 inches.
That is the practical consequence. Fittings, flanges, supports and threading dies are sized to the outside diameter, so they fit any schedule of the same trade size. Flow, pressure drop and anything that has to pass through the pipe depend on the inside diameter, which changes with every schedule. Order by trade size and schedule; work your hydraulics from the bore.
Frequently asked questions
What is the wall thickness of 24 inch schedule 5s pipe?
0.218 inches (5.54 mm). The outside diameter is 24.000 inches (609.60 mm) whatever the schedule, so this wall leaves an inside diameter of 23.564 inches.
What is the inside diameter of 24 inch schedule 5s pipe?
23.564 inches (598.52 mm). Inside diameter is outside diameter minus twice the wall: 24.000 - 2 x 0.218 = 23.564 inches.
Is 24 inch pipe actually 24 inches?
No. NPS 24 is a trade size, not a measurement. The pipe measures 24.000 inches across the outside and 23.564 inches across the bore in this schedule. Only the outside diameter is fixed across schedules.
Where these figures come from
Dimensions are as defined by ASME B36.19M (stainless steel pipe). This site is an independent reference and is not affiliated with, endorsed by or approved by any standards body.
Every value on this page was cross-checked against 2 independent published sources: