ASME B36.10M (welded and seamless wrought steel pipe) · DN 25
Outside diameter 1.315" (33.40 mm), wall 0.133" (3.38 mm), inside diameter 1.049" (26.64 mm), 1.68 lb per foot.
| Trade size | NPS 1 · DN 25 |
|---|---|
| Schedule | Schedule 40 · same wall as STD, 40S |
| Standard | ASME B36.10M (welded and seamless wrought steel pipe) |
| Outside diameter | 1.315" · 33.40 mm |
| Wall thickness | 0.133" · 3.38 mm |
| Inside diameter | 1.049" · 26.64 mm |
| Weight, plain end | 1.68 lb/ft · 2.5 kg/m |
Cross-check: the standard plain-end weight formula W = 10.6802 x t x (OD - t) gives 1.68 lb/ft here, 0.1% from the published 1.68 lb/ft. The published figure is the one printed above.
NPS 1 schedule 40 pipe measures 1.315 in (33.40 mm) across the outside with a 0.133 in wall, so the bore is 1.049 in (26.64 mm). That bore gives a flow area of 0.8643 in² and holds 0.04490 US gallons per foot (0.5576 litres per metre). The outside diameter is 9.9 times the wall, and the steel itself has a cross-section of 0.4939 in² and weighs 1.68 lb per foot plain end. One trade size up, NPS 1-1/4 in the same schedule carries 1.73 times the flow area.
Schedule 30 is the next lighter wall at NPS 1: 0.114 in, 0.019 in thinner, which opens the bore to 1.087 in and adds 7.4% to the flow area, for 13% less weight per foot.
Schedule 80 is the next heavier wall at NPS 1: 0.179 in, 0.046 in thicker, which narrows the bore to 0.957 in and cuts 17% from the flow area, for 29% more weight per foot.
Next trade size up in this schedule: NPS 1-1/4 schedule 40, bore 1.380 in.
| Flow area | 0.8643 in² |
|---|---|
| Capacity | 0.04490 US gal/ft · 0.5576 L/m |
| Metal area | 0.4939 in² |
| Moment of inertia | 0.08734 in⁴ |
| Section modulus | 0.1328 in³ |
| Radius of gyration | 0.4205 in |
| Outside surface | 0.3443 ft² per foot |
Plain geometry of a hollow circle with OD = 1.315 in and ID = 1.049 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 40 the wall is 0.133 inches, so the bore comes out at 1.049 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 80 · XS, 80S | 0.179 | 0.957 | 2.17 |
| Schedule 160 | 0.250 | 0.815 | 2.85 |
| Double extra strong (XXS) | 0.358 | 0.599 | 3.66 |
0.133 inches (3.38 mm). The outside diameter is 1.315 inches (33.40 mm) whatever the schedule, so this wall leaves an inside diameter of 1.049 inches.
1.049 inches (26.64 mm). Inside diameter is outside diameter minus twice the wall: 1.315 - 2 x 0.133 = 1.049 inches.
No. NPS 1 is a trade size, not a measurement. The pipe measures 1.315 inches across the outside and 1.049 inches across the bore in this schedule. Only the outside diameter is fixed across schedules.
1.68 pounds per foot plain end (2.5 kg per metre), for carbon steel. The figure excludes coatings, linings and fittings.
Yes, at NPS 1. STD and 40S are the same 0.133 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