Dimensions
Cross-check: the standard plain-end weight formula W = 10.6802 x t x (OD - t) gives 53.16 lb/ft here, 0.1% from the published 53.21 lb/ft. The published figure is the one printed above.
NPS 6 double extra strong (xxs) in numbers
NPS 6 double extra strong (xxs) pipe measures 6.625 in (168.27 mm) across the outside with a 0.864 in wall, so the bore is 4.897 in (124.37 mm). That bore gives a flow area of 18.83 in² and holds 0.9784 US gallons per foot (12.15 litres per metre). The outside diameter is 7.7 times the wall, and the steel itself has a cross-section of 15.64 in² and weighs 53.21 lb per foot plain end. One trade size up, NPS 8 in the same schedule carries 1.97 times the flow area.
Schedule 160 is the next lighter wall at NPS 6: 0.719 in, 0.145 in thinner, which opens the bore to 5.187 in and adds 12% to the flow area, for 15% less weight per foot.
Next trade size up in this schedule: NPS 8 double extra strong (xxs), bore 6.875 in.
Worked out from the dimensions
Plain geometry of a hollow circle with OD = 6.625 in and ID = 4.897 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 6 inch pipe is not 6 inches
Nominal Pipe Size is a label, not a measurement. NPS 6 pipe has an outside diameter of 6.625 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 0.864 inches, so the bore comes out at 4.897 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 6
Same outside diameter of 6.625 inches throughout - only the wall and the bore move.
Frequently asked questions
What is the wall thickness of 6 inch double extra strong (xxs) pipe?
0.864 inches (21.95 mm). The outside diameter is 6.625 inches (168.27 mm) whatever the schedule, so this wall leaves an inside diameter of 4.897 inches.
What is the inside diameter of 6 inch double extra strong (xxs) pipe?
4.897 inches (124.37 mm). Inside diameter is outside diameter minus twice the wall: 6.625 - 2 x 0.864 = 4.897 inches.
Is 6 inch pipe actually 6 inches?
No. NPS 6 is a trade size, not a measurement. The pipe measures 6.625 inches across the outside and 4.897 inches across the bore in this schedule. Only the outside diameter is fixed across schedules.
How much does 6 inch double extra strong (xxs) pipe weigh?
53.21 pounds per foot plain end (79.22 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: