Dimensions
Cross-check: the standard plain-end weight formula W = 10.6802 x t x (OD - t) gives 88.63 lb/ft here, 0.1% from the published 88.71 lb/ft. The published figure is the one printed above.
NPS 12 schedule 80 in numbers
NPS 12 schedule 80 pipe measures 12.750 in (323.85 mm) across the outside with a 0.688 in wall, so the bore is 11.374 in (288.89 mm). That bore gives a flow area of 101.6 in² and holds 5.278 US gallons per foot (65.55 litres per metre). The outside diameter is 18.5 times the wall, and the steel itself has a cross-section of 26.07 in² and weighs 88.71 lb per foot plain end. One trade size up, NPS 14 in the same schedule carries 1.21 times the flow area.
Schedule 60 is the next lighter wall at NPS 12: 0.562 in, 0.126 in thinner, which opens the bore to 11.626 in and adds 4.5% to the flow area, for 17% less weight per foot.
Schedule 100 is the next heavier wall at NPS 12: 0.844 in, 0.156 in thicker, which narrows the bore to 11.062 in and cuts 5.4% from the flow area, for 21% more weight per foot.
Next trade size up in this schedule: NPS 14 schedule 80, bore 12.500 in.
Worked out from the dimensions
Plain geometry of a hollow circle with OD = 12.750 in and ID = 11.374 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 12 inch pipe is not 12 inches
Nominal Pipe Size is a label, not a measurement. NPS 12 pipe has an outside diameter of 12.750 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 0.688 inches, so the bore comes out at 11.374 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 12
Same outside diameter of 12.750 inches throughout - only the wall and the bore move.
Frequently asked questions
What is the wall thickness of 12 inch schedule 80 pipe?
0.688 inches (17.48 mm). The outside diameter is 12.750 inches (323.85 mm) whatever the schedule, so this wall leaves an inside diameter of 11.374 inches.
What is the inside diameter of 12 inch schedule 80 pipe?
11.374 inches (288.89 mm). Inside diameter is outside diameter minus twice the wall: 12.750 - 2 x 0.688 = 11.374 inches.
Is 12 inch pipe actually 12 inches?
No. NPS 12 is a trade size, not a measurement. The pipe measures 12.750 inches across the outside and 11.374 inches across the bore in this schedule. Only the outside diameter is fixed across schedules.
How much does 12 inch schedule 80 pipe weigh?
88.71 pounds per foot plain end (132.05 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:
Sources disagree here. Published tables split on the last digit here - 0.688 in (b3610m-etb), 0.688 in (b3610m-fbc), 0.687 in (b3610m-wikipedia); 17.48 mm (b3610m-ferrobend), 17.48 mm (b3610m-wermac), 17.45 mm (b3610m-wikipedia). The figure printed is 0.688 in (17.48 mm), carried by the majority of the sources. The two readings describe the same wall: they differ by less than a thousandth of an inch, far inside the mill tolerance of minus 12.5 percent on wall thickness.
Last-digit inch walls across the whole table: 0.594, 0.688, 0.719, 0.844, 0.938, 1.094, 1.219, 1.438, 1.969, 2.344 in (b3610m-fbc) against 0.593, 0.687, 0.718, 0.843, 0.937, 1.093, 1.218, 1.437, 1.968, 2.343 in (b3610m-wikipedia). Two families of inch figures are in circulation, one a thousandth of an inch below the other, and they come from rounding the millimetre wall the standard tabulates rather than from any difference in the pipe. The higher family is what the majority of the sources read here carry and is what this site prints; the affected rows say so individually. Nothing turns on the choice: the wall tolerance is minus 12.5 percent, which at a half-inch wall is sixty times the gap.
NPS 14 extra strong (XS): 0.469 in (b3610m-fbc) against 0.500 in (b3610m-etb) against 0.500 in (b3610m-wikipedia). 0.500 in is printed here. Two of the three inch sources give it, both millimetre sources give 12.70 mm which is 0.500 in, and extra strong is a 0.500 in wall at every size from NPS 12 up. The 0.469 in reading looks like a misplaced row in that one chart, but it is recorded rather than deleted.