ASME B36.10M (welded and seamless wrought steel pipe) · DN 300
Outside diameter 12.750" (323.85 mm), wall 0.406" (10.31 mm), inside diameter 11.938" (303.23 mm), 53.57 lb per foot.
| Trade size | NPS 12 · DN 300 |
|---|---|
| Schedule | Schedule 40 |
| Standard | ASME B36.10M (welded and seamless wrought steel pipe) |
| Outside diameter | 12.750" · 323.85 mm · designated 323.8 mm in the metric column |
| Wall thickness | 0.406" · 10.31 mm |
| Inside diameter | 11.938" · 303.23 mm |
| Weight, plain end | 53.57 lb/ft · 79.71 kg/m |
Cross-check: the standard plain-end weight formula W = 10.6802 x t x (OD - t) gives 53.53 lb/ft here, 0.1% from the published 53.57 lb/ft. The published figure is the one printed above.
NPS 12 schedule 40 pipe measures 12.750 in (323.85 mm) across the outside with a 0.406 in wall, so the bore is 11.938 in (303.23 mm). That bore gives a flow area of 111.9 in² and holds 5.815 US gallons per foot (72.21 litres per metre). The outside diameter is 31.4 times the wall, and the steel itself has a cross-section of 15.74 in² and weighs 53.57 lb per foot plain end. One trade size up, NPS 14 in the same schedule carries 1.21 times the flow area.
Standard wall (STD) is the next lighter wall at NPS 12: 0.375 in, 0.031 in thinner, which opens the bore to 12.000 in and adds 1.0% to the flow area, for 7.4% less weight per foot.
Extra strong (XS) is the next heavier wall at NPS 12: 0.500 in, 0.094 in thicker, which narrows the bore to 11.750 in and cuts 3.1% from the flow area, for 22% more weight per foot.
Next trade size up in this schedule: NPS 14 schedule 40, bore 13.124 in.
| Flow area | 111.9 in² |
|---|---|
| Capacity | 5.815 US gal/ft · 72.21 L/m |
| Metal area | 15.74 in² |
| Moment of inertia | 300.2 in⁴ |
| Section modulus | 47.09 in³ |
| Radius of gyration | 4.367 in |
| Outside surface | 3.338 ft² per foot |
Plain geometry of a hollow circle with OD = 12.750 in and ID = 11.938 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 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 40 the wall is 0.406 inches, so the bore comes out at 11.938 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 12.750 inches throughout - only the wall and the bore move.
| Schedule | Wall (in) | ID (in) | Weight (lb/ft) |
|---|---|---|---|
| Schedule 5 · 5S | 0.156 | 12.438 | 21.00 |
| Schedule 10 · 10S | 0.180 | 12.390 | 24.19 |
| Schedule 20 | 0.250 | 12.250 | 33.41 |
| Schedule 30 | 0.330 | 12.090 | 43.81 |
| Schedule 60 | 0.562 | 11.626 | 73.22 |
| Schedule 80 | 0.688 | 11.374 | 88.71 |
| Schedule 100 | 0.844 | 11.062 | 107.42 |
| Schedule 140 | 1.125 | 10.500 | 139.81 |
| Schedule 160 | 1.312 | 10.126 | 160.42 |
| Standard wall (STD) · 40S | 0.375 | 12.000 | 49.61 |
| Extra strong (XS) · 80S | 0.500 | 11.750 | 65.48 |
| Double extra strong (XXS) · 120 | 1.000 | 10.750 | 125.61 |
0.406 inches (10.31 mm). The outside diameter is 12.750 inches (323.85 mm) whatever the schedule, so this wall leaves an inside diameter of 11.938 inches.
11.938 inches (303.23 mm). Inside diameter is outside diameter minus twice the wall: 12.750 - 2 x 0.406 = 11.938 inches.
No. NPS 12 is a trade size, not a measurement. The pipe measures 12.750 inches across the outside and 11.938 inches across the bore in this schedule. Only the outside diameter is fixed across schedules.
53.57 pounds per foot plain end (79.71 kg per metre), for carbon steel. The figure excludes coatings, linings and fittings.
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:
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