Dimensions
Cross-check: the standard plain-end weight formula W = 10.6802 x t x (OD - t) gives 1.71 lb/ft here, 0.3% from the published 1.71 lb/ft. The published figure is the one printed above.
NPS 1/2 double extra strong (xxs) in numbers
NPS 1/2 double extra strong (xxs) pipe measures 0.840 in (21.34 mm) across the outside with a 0.294 in wall, so the bore is 0.252 in (6.40 mm). That bore gives a flow area of 0.04988 in² and holds 0.002591 US gallons per foot (0.03218 litres per metre). The outside diameter is 2.9 times the wall, and the steel itself has a cross-section of 0.5043 in² and weighs 1.71 lb per foot plain end. One trade size up, NPS 3/4 in the same schedule carries 2.97 times the flow area.
Schedule 160 is the next lighter wall at NPS 1/2: 0.188 in, 0.106 in thinner, which opens the bore to 0.464 in and adds 239% to the flow area, for 23% less weight per foot.
Next trade size up in this schedule: NPS 3/4 double extra strong (xxs), bore 0.434 in.
Worked out from the dimensions
Plain geometry of a hollow circle with OD = 0.840 in and ID = 0.252 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 1/2 inch pipe is not 1/2 inches
Nominal Pipe Size is a label, not a measurement. NPS 1/2 pipe has an outside diameter of 0.840 inches, and it keeps that outside diameter in every schedule made. What the schedule number changes is the wall: at double extra strong (xxs) the wall is 0.294 inches, so the bore comes out at 0.252 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 1/2
Same outside diameter of 0.840 inches throughout - only the wall and the bore move.
Frequently asked questions
What is the wall thickness of 1/2 inch double extra strong (xxs) pipe?
0.294 inches (7.47 mm). The outside diameter is 0.840 inches (21.34 mm) whatever the schedule, so this wall leaves an inside diameter of 0.252 inches.
What is the inside diameter of 1/2 inch double extra strong (xxs) pipe?
0.252 inches (6.40 mm). Inside diameter is outside diameter minus twice the wall: 0.840 - 2 x 0.294 = 0.252 inches.
Is 1/2 inch pipe actually 1/2 inches?
No. NPS 1/2 is a trade size, not a measurement. The pipe measures 0.840 inches across the outside and 0.252 inches across the bore in this schedule. Only the outside diameter is fixed across schedules.
How much does 1/2 inch double extra strong (xxs) pipe weigh?
1.71 pounds per foot plain end (2.55 kg per metre), for carbon steel. The figure excludes coatings, linings and fittings.
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: