Dimensions
Cross-check: the standard plain-end weight formula W = 10.6802 x t x (OD - t) gives 28.55 lb/ft here, 0.1% from the published 28.58 lb/ft. The published figure is the one printed above.
NPS 8 schedule 40 in numbers
NPS 8 schedule 40 pipe measures 8.625 in (219.07 mm) across the outside with a 0.322 in wall, so the bore is 7.981 in (202.71 mm). That bore gives a flow area of 50.03 in² and holds 2.599 US gallons per foot (32.28 litres per metre). The outside diameter is 26.8 times the wall, and the steel itself has a cross-section of 8.399 in² and weighs 28.58 lb per foot plain end. One trade size up, NPS 10 in the same schedule carries 1.58 times the flow area.
Schedule 30 is the next lighter wall at NPS 8: 0.277 in, 0.045 in thinner, which opens the bore to 8.071 in and adds 2.3% to the flow area, for 14% less weight per foot.
Schedule 60 is the next heavier wall at NPS 8: 0.406 in, 0.084 in thicker, which narrows the bore to 7.813 in and cuts 4.2% from the flow area, for 25% more weight per foot.
Next trade size up in this schedule: NPS 10 schedule 40, bore 10.020 in.
Worked out from the dimensions
Plain geometry of a hollow circle with OD = 8.625 in and ID = 7.981 in: flow area π/4·ID², metal area π/4·(OD² − ID²), moment of inertia π/64·(OD⁴ − ID⁴), section modulus I ÷ (OD/2), radius of gyration √(I ÷ metal area), capacity flow area × 12 ÷ 231 (231 in³ to the US gallon). Nominal dimensions, so mill tolerance and corrosion allowance are not included.
Why 8 inch pipe is not 8 inches
Nominal Pipe Size is a label, not a measurement. NPS 8 pipe has an outside diameter of 8.625 inches, and it keeps that outside diameter in every schedule made. What the schedule number changes is the wall: at schedule 40 the wall is 0.322 inches, so the bore comes out at 7.981 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.
Other schedules in NPS 8
Same outside diameter of 8.625 inches throughout - only the wall and the bore move.
Frequently asked questions
What is the wall thickness of 8 inch schedule 40 pipe?
0.322 inches (8.18 mm). The outside diameter is 8.625 inches (219.07 mm) whatever the schedule, so this wall leaves an inside diameter of 7.981 inches.
What is the inside diameter of 8 inch schedule 40 pipe?
7.981 inches (202.71 mm). Inside diameter is outside diameter minus twice the wall: 8.625 - 2 x 0.322 = 7.981 inches.
Is 8 inch pipe actually 8 inches?
No. NPS 8 is a trade size, not a measurement. The pipe measures 8.625 inches across the outside and 7.981 inches across the bore in this schedule. Only the outside diameter is fixed across schedules.
How much does 8 inch schedule 40 pipe weigh?
28.58 pounds per foot plain end (42.55 kg per metre), for carbon steel. The figure excludes coatings, linings and fittings.
Is schedule 40 the same as STD or 40S at this size?
Yes, at NPS 8. STD and 40S are the same 0.322 inch wall here. That coincidence is per size and does not hold everywhere: standard wall and schedule 40 part company above NPS 10, and extra strong and schedule 80 part company above NPS 8.
Where this table stops
This table runs from NPS 1/8 to NPS 24 and stops there. ASME B36.10M itself continues to NPS 80; those larger sizes are not carried here, so a size above NPS 24 is missing rather than undefined.
Where these figures come from
Dimensions are as defined by ASME B36.10M (welded and seamless wrought 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 5 independent published sources: