ASME B36.10M (welded and seamless wrought steel pipe) · DN 25
Outside diameter 1.315" (33.40 mm), wall 0.179" (4.55 mm), inside diameter 0.957" (24.30 mm), 2.17 lb per foot.
| Trade size | NPS 1 · DN 25 |
|---|---|
| Schedule | Schedule 80 · same wall as XS, 80S |
| Standard | ASME B36.10M (welded and seamless wrought steel pipe) |
| Outside diameter | 1.315" · 33.40 mm |
| Wall thickness | 0.179" · 4.55 mm |
| Inside diameter | 0.957" · 24.30 mm |
| Weight, plain end | 2.17 lb/ft · 3.24 kg/m |
Cross-check: the standard plain-end weight formula W = 10.6802 x t x (OD - t) gives 2.17 lb/ft here, 0.1% from the published 2.17 lb/ft. The published figure is the one printed above.
NPS 1 schedule 80 pipe measures 1.315 in (33.40 mm) across the outside with a 0.179 in wall, so the bore is 0.957 in (24.30 mm). That bore gives a flow area of 0.7193 in² and holds 0.03737 US gallons per foot (0.4641 litres per metre). The outside diameter is 7.3 times the wall, and the steel itself has a cross-section of 0.6388 in² and weighs 2.17 lb per foot plain end. One trade size up, NPS 1-1/4 in the same schedule carries 1.78 times the flow area.
Schedule 40 is the next lighter wall at NPS 1: 0.133 in, 0.046 in thinner, which opens the bore to 1.049 in and adds 20% to the flow area, for 23% less weight per foot.
Schedule 160 is the next heavier wall at NPS 1: 0.250 in, 0.071 in thicker, which narrows the bore to 0.815 in and cuts 27% from the flow area, for 31% more weight per foot.
Next trade size up in this schedule: NPS 1-1/4 schedule 80, bore 1.278 in.
| Flow area | 0.7193 in² |
|---|---|
| Capacity | 0.03737 US gal/ft · 0.4641 L/m |
| Metal area | 0.6388 in² |
| Moment of inertia | 0.1056 in⁴ |
| Section modulus | 0.1606 in³ |
| Radius of gyration | 0.4066 in |
| Outside surface | 0.3443 ft² per foot |
Plain geometry of a hollow circle with OD = 1.315 in and ID = 0.957 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.
Nominal Pipe Size is a label, not a measurement. NPS 1 pipe has an outside diameter of 1.315 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 0.179 inches, so the bore comes out at 0.957 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.
Same outside diameter of 1.315 inches throughout - only the wall and the bore move.
| Schedule | Wall (in) | ID (in) | Weight (lb/ft) |
|---|---|---|---|
| Schedule 5 · 5S | 0.065 | 1.185 | 0.87 |
| Schedule 10 · 10S | 0.109 | 1.097 | 1.41 |
| Schedule 30 | 0.114 | 1.087 | 1.46 |
| Schedule 40 · STD, 40S | 0.133 | 1.049 | 1.68 |
| Schedule 160 | 0.250 | 0.815 | 2.85 |
| Double extra strong (XXS) | 0.358 | 0.599 | 3.66 |
0.179 inches (4.55 mm). The outside diameter is 1.315 inches (33.40 mm) whatever the schedule, so this wall leaves an inside diameter of 0.957 inches.
0.957 inches (24.30 mm). Inside diameter is outside diameter minus twice the wall: 1.315 - 2 x 0.179 = 0.957 inches.
No. NPS 1 is a trade size, not a measurement. The pipe measures 1.315 inches across the outside and 0.957 inches across the bore in this schedule. Only the outside diameter is fixed across schedules.
2.17 pounds per foot plain end (3.24 kg per metre), for carbon steel. The figure excludes coatings, linings and fittings.
Yes, at NPS 1. XS and 80S are the same 0.179 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.
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.
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