Dimensions
Cross-check: the standard plain-end weight formula W = 10.6802 x t x (OD - t) gives 0.19 lb/ft here, 1.9% from the published 0.19 lb/ft. The published figure is the one printed above.
NPS 1/8 schedule 10 in numbers
NPS 1/8 schedule 10 pipe measures 0.405 in (10.29 mm) across the outside with a 0.049 in wall, so the bore is 0.307 in (7.81 mm). That bore gives a flow area of 0.07402 in² and holds 0.003845 US gallons per foot (0.04776 litres per metre). The outside diameter is 8.3 times the wall, and the steel itself has a cross-section of 0.05480 in² and weighs 0.19 lb per foot plain end. One trade size up, NPS 1/4 in the same schedule carries 1.78 times the flow area.
Schedule 30 is the next heavier wall at NPS 1/8: 0.057 in, 0.008 in thicker, which narrows the bore to 0.291 in and cuts 10% from the flow area, for 11% more weight per foot.
Next trade size up in this schedule: NPS 1/4 schedule 10, bore 0.410 in.
Worked out from the dimensions
Plain geometry of a hollow circle with OD = 0.405 in and ID = 0.307 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 1/8 inch pipe is not 1/8 inches
Nominal Pipe Size is a label, not a measurement. NPS 1/8 pipe has an outside diameter of 0.405 inches, and it keeps that outside diameter in every schedule made. What the schedule number changes is the wall: at schedule 10 the wall is 0.049 inches, so the bore comes out at 0.307 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 1/8
Same outside diameter of 0.405 inches throughout - only the wall and the bore move.
Frequently asked questions
What is the wall thickness of 1/8 inch schedule 10 pipe?
0.049 inches (1.24 mm). The outside diameter is 0.405 inches (10.29 mm) whatever the schedule, so this wall leaves an inside diameter of 0.307 inches.
What is the inside diameter of 1/8 inch schedule 10 pipe?
0.307 inches (7.81 mm). Inside diameter is outside diameter minus twice the wall: 0.405 - 2 x 0.049 = 0.307 inches.
Is 1/8 inch pipe actually 1/8 inches?
No. NPS 1/8 is a trade size, not a measurement. The pipe measures 0.405 inches across the outside and 0.307 inches across the bore in this schedule. Only the outside diameter is fixed across schedules.
How much does 1/8 inch schedule 10 pipe weigh?
0.19 pounds per foot plain end (0.28 kg per metre), for carbon steel. The figure excludes coatings, linings and fittings.
Is schedule 10 the same as 10S at this size?
Yes, at NPS 1/8. 10S is the same 0.049 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
3 schedules at NPS 1/8 appear in only one of the published tables cross-checked for this section, so they are named rather than printed: 160, XXS, 5S. 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 4 independent published sources: