Pipe schedules · NPS 2-1/2
ASME B36.10M (welded and seamless wrought steel pipe) · DN 65
2-1/2 inch Schedule 80 pipe
Outside diameter 2.875" (73.02 mm), wall 0.276" (7.01 mm), inside diameter 2.323" (59.00 mm), 7.67 lb per foot.
Dimensions
Cross-check: the standard plain-end weight formula W = 10.6802 x t x (OD - t) gives 7.66 lb/ft here, 0.1% from the published 7.67 lb/ft. The published figure is the one printed above.
NPS 2-1/2 schedule 80 in numbers
NPS 2-1/2 schedule 80 pipe measures 2.875 in (73.02 mm) across the outside with a 0.276 in wall, so the bore is 2.323 in (59.00 mm). That bore gives a flow area of 4.238 in² and holds 0.2202 US gallons per foot (2.734 litres per metre). The outside diameter is 10.4 times the wall, and the steel itself has a cross-section of 2.254 in² and weighs 7.67 lb per foot plain end. One trade size up, NPS 3 in the same schedule carries 1.56 times the flow area.
Schedule 40 is the next lighter wall at NPS 2-1/2: 0.203 in, 0.073 in thinner, which opens the bore to 2.469 in and adds 13% to the flow area, for 24% less weight per foot.
Schedule 160 is the next heavier wall at NPS 2-1/2: 0.375 in, 0.099 in thicker, which narrows the bore to 2.125 in and cuts 16% from the flow area, for 31% more weight per foot.
Next trade size up in this schedule: NPS 3 schedule 80, bore 2.900 in.
Worked out from the dimensions
Plain geometry of a hollow circle with OD = 2.875 in and ID = 2.323 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 2-1/2 inch pipe is not 2-1/2 inches
Nominal Pipe Size is a label, not a measurement. NPS 2-1/2 pipe has an outside diameter of 2.875 inches, and it keeps that outside diameter in every schedule made. What the schedule number changes is the wall: at schedule 80 the wall is 0.276 inches, so the bore comes out at 2.323 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 2-1/2
Same outside diameter of 2.875 inches throughout - only the wall and the bore move.
Frequently asked questions
What is the wall thickness of 2-1/2 inch schedule 80 pipe?
0.276 inches (7.01 mm). The outside diameter is 2.875 inches (73.02 mm) whatever the schedule, so this wall leaves an inside diameter of 2.323 inches.
What is the inside diameter of 2-1/2 inch schedule 80 pipe?
2.323 inches (59.00 mm). Inside diameter is outside diameter minus twice the wall: 2.875 - 2 x 0.276 = 2.323 inches.
Is 2-1/2 inch pipe actually 2-1/2 inches?
No. NPS 2-1/2 is a trade size, not a measurement. The pipe measures 2.875 inches across the outside and 2.323 inches across the bore in this schedule. Only the outside diameter is fixed across schedules.
How much does 2-1/2 inch schedule 80 pipe weigh?
7.67 pounds per foot plain end (11.41 kg per metre), for carbon steel. The figure excludes coatings, linings and fittings.
Is schedule 80 the same as XS or 80S at this size?
Yes, at NPS 2-1/2. XS and 80S are the same 0.276 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.
Not published here
One schedule at NPS 2-1/2 appears in only one of the published tables cross-checked for this section, so it is named rather than printed: 120. Everything shown above carries at least two independent sources.
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:
Nearby sizes
Schedule 80 in other trade sizes