STD vs XS Pipe
Standard weight against Extra Strong: identical to Schedules 40 and 80 in small bore, and deliberately not identical once the pipe gets large.
- Sizes with both
- 34
- XS weight penalty
- +35% on average
- STD wall above NPS 10
- 0.375 in, constant
- XS wall above NPS 8
- 0.500 in, constant
Short answer. Standard weight and Extra Strong are the pre-schedule wall designations that survived into modern practice. STD tracks Schedule 40 up to NPS 11 and XS tracks Schedule 80 up to NPS 11; above those sizes both freeze at a constant wall while the numbered schedules keep climbing. XS is the heavier of the two in every size.
Two series that agree, then stop agreeing
STD and Schedule 40 are the same wall in every size from NPS 1/8 through NPS 11. From NPS 12 upward they diverge: STD holds at 0.375 in for every larger size, while Schedule 40 keeps thickening with diameter.
XS and Schedule 80 behave the same way one size earlier. They match through NPS 11, and from NPS 10 up XS holds at 0.500 in while Schedule 80 climbs. This is why a large-bore line called out as “XS” and one called out as “Schedule 80” are not the same pipe, and why the two must never be treated as interchangeable on a large-diameter isometric.
STD = Sch 40 through NPS 11 · XS = Sch 80 through NPS 11
Dimensions are given in inches, with the millimetre equivalent beneath in grey.
| NPS | OD | STD wall | XS wall | STD bore | XS bore | STD weight | XS weight | Weight change | Flow area change |
|---|---|---|---|---|---|---|---|---|---|
| NPS 1/8 | 0.40510.29 mm | 0.0681.73 mm | 0.0952.41 mm | 0.2696.83 mm | 0.2155.46 mm | 0.240.36 kg/m | 0.310.47 kg/m | +29% | -36% |
| NPS 1/4 | 0.54013.72 mm | 0.0882.24 mm | 0.1193.02 mm | 0.3649.25 mm | 0.3027.67 mm | 0.420.63 kg/m | 0.540.80 kg/m | +26% | -31% |
| NPS 3/8 | 0.67517.14 mm | 0.0912.31 mm | 0.1263.20 mm | 0.49312.52 mm | 0.42310.74 mm | 0.570.84 kg/m | 0.741.10 kg/m | +30% | -26% |
| NPS 1/2 | 0.84021.34 mm | 0.1092.77 mm | 0.1473.73 mm | 0.62215.80 mm | 0.54613.87 mm | 0.851.27 kg/m | 1.091.62 kg/m | +28% | -23% |
| NPS 3/4 | 1.05026.67 mm | 0.1132.87 mm | 0.1543.91 mm | 0.82420.93 mm | 0.74218.85 mm | 1.131.68 kg/m | 1.472.19 kg/m | +30% | -19% |
| NPS 1 | 1.31533.40 mm | 0.1333.38 mm | 0.1794.55 mm | 1.04926.64 mm | 0.95724.31 mm | 1.682.50 kg/m | 2.173.23 kg/m | +29% | -17% |
| NPS 1 1/4 | 1.66042.16 mm | 0.1403.56 mm | 0.1914.85 mm | 1.38035.05 mm | 1.27832.46 mm | 2.273.38 kg/m | 3.004.46 kg/m | +32% | -14% |
| NPS 1 1/2 | 1.90048.26 mm | 0.1453.68 mm | 0.2005.08 mm | 1.61040.89 mm | 1.50038.10 mm | 2.724.04 kg/m | 3.635.40 kg/m | +34% | -13% |
| NPS 2 | 2.37560.32 mm | 0.1543.91 mm | 0.2185.54 mm | 2.06752.50 mm | 1.93949.25 mm | 3.655.44 kg/m | 5.027.47 kg/m | +37% | -12% |
| NPS 2 1/2 | 2.87573.02 mm | 0.2035.16 mm | 0.2767.01 mm | 2.46962.71 mm | 2.32359.00 mm | 5.798.62 kg/m | 7.6611.40 kg/m | +32% | -11% |
| NPS 3 | 3.50088.90 mm | 0.2165.49 mm | 0.3007.62 mm | 3.06877.93 mm | 2.90073.66 mm | 7.5811.27 kg/m | 10.2515.26 kg/m | +35% | -11% |
| NPS 3 1/2 | 4.000101.60 mm | 0.2265.74 mm | 0.3188.08 mm | 3.54890.12 mm | 3.36485.45 mm | 9.1113.56 kg/m | 12.5118.61 kg/m | +37% | -10% |
| NPS 4 | 4.500114.30 mm | 0.2376.02 mm | 0.3378.56 mm | 4.026102.26 mm | 3.82697.18 mm | 10.7916.06 kg/m | 14.9822.30 kg/m | +39% | -10% |
| NPS 4 1/2 | 5.000127.00 mm | 0.2476.27 mm | 0.3559.02 mm | 4.506114.45 mm | 4.290108.97 mm | 12.5418.66 kg/m | 17.6126.21 kg/m | +40% | -9% |
| NPS 5 | 5.563141.30 mm | 0.2586.55 mm | 0.3759.52 mm | 5.047128.19 mm | 4.813122.25 mm | 14.6221.75 kg/m | 20.7830.92 kg/m | +42% | -9% |
| NPS 6 | 6.625168.27 mm | 0.2807.11 mm | 0.43210.97 mm | 6.065154.05 mm | 5.761146.33 mm | 18.9728.24 kg/m | 28.5742.52 kg/m | +51% | -10% |
| NPS 7 | 7.625193.67 mm | 0.3017.65 mm | 0.50012.70 mm | 7.023178.38 mm | 6.625168.27 mm | 23.5435.04 kg/m | 38.0556.62 kg/m | +62% | -11% |
| NPS 8 | 8.625219.07 mm | 0.3228.18 mm | 0.50012.70 mm | 7.981202.72 mm | 7.625193.67 mm | 28.5542.49 kg/m | 43.3964.57 kg/m | +52% | -9% |
| NPS 9 | 9.625244.47 mm | 0.3428.69 mm | 0.50012.70 mm | 8.941227.10 mm | 8.625219.07 mm | 33.9150.46 kg/m | 48.7372.52 kg/m | +44% | -7% |
| NPS 10 | 10.750273.05 mm | 0.3659.27 mm | 0.50012.70 mm | 10.020254.51 mm | 9.750247.65 mm | 40.4860.25 kg/m | 54.7481.46 kg/m | +35% | -5% |
| NPS 11 | 11.750298.45 mm | 0.3759.52 mm | 0.50012.70 mm | 11.000279.40 mm | 10.750273.05 mm | 45.5667.80 kg/m | 60.0889.40 kg/m | +32% | -4% |
| NPS 12 | 12.750323.85 mm | 0.3759.52 mm | 0.50012.70 mm | 12.000304.80 mm | 11.750298.45 mm | 49.5673.76 kg/m | 65.4297.35 kg/m | +32% | -4% |
| NPS 14 | 14.000355.60 mm | 0.3759.52 mm | 0.50012.70 mm | 13.250336.55 mm | 13.000330.20 mm | 54.5781.21 kg/m | 72.09107.28 kg/m | +32% | -4% |
| NPS 16 | 16.000406.40 mm | 0.3759.52 mm | 0.50012.70 mm | 15.250387.35 mm | 15.000381.00 mm | 62.5893.13 kg/m | 82.77123.18 kg/m | +32% | -3% |
| NPS 18 | 18.000457.20 mm | 0.3759.52 mm | 0.50012.70 mm | 17.250438.15 mm | 17.000431.80 mm | 70.59105.05 kg/m | 93.45139.07 kg/m | +32% | -3% |
| NPS 20 | 20.000508.00 mm | 0.3759.52 mm | 0.50012.70 mm | 19.250488.95 mm | 19.000482.60 mm | 78.60116.97 kg/m | 104.13154.97 kg/m | +32% | -3% |
| NPS 22 | 22.000558.80 mm | 0.3759.52 mm | 0.50012.70 mm | 21.250539.75 mm | 21.000533.40 mm | 86.61128.89 kg/m | 114.81170.86 kg/m | +33% | -2% |
| NPS 24 | 24.000609.60 mm | 0.3759.52 mm | 0.50012.70 mm | 23.250590.55 mm | 23.000584.20 mm | 94.62140.81 kg/m | 125.49186.75 kg/m | +33% | -2% |
| NPS 26 | 26.000660.40 mm | 0.3759.52 mm | 0.50012.70 mm | 25.250641.35 mm | 25.000635.00 mm | 102.63152.73 kg/m | 136.17202.65 kg/m | +33% | -2% |
| NPS 28 | 28.000711.20 mm | 0.3759.52 mm | 0.50012.70 mm | 27.250692.15 mm | 27.000685.80 mm | 110.64164.65 kg/m | 146.85218.54 kg/m | +33% | -2% |
| NPS 30 | 30.000762.00 mm | 0.3759.52 mm | 0.50012.70 mm | 29.250742.95 mm | 29.000736.60 mm | 118.65176.57 kg/m | 157.53234.43 kg/m | +33% | -2% |
| NPS 32 | 32.000812.80 mm | 0.3759.52 mm | 0.50012.70 mm | 31.250793.75 mm | 31.000787.40 mm | 126.66188.49 kg/m | 168.21250.33 kg/m | +33% | -2% |
| NPS 34 | 34.000863.60 mm | 0.3759.52 mm | 0.50012.70 mm | 33.250844.55 mm | 33.000838.20 mm | 134.67200.41 kg/m | 178.89266.22 kg/m | +33% | -1% |
| NPS 36 | 36.000914.40 mm | 0.3759.52 mm | 0.50012.70 mm | 35.250895.35 mm | 35.000889.00 mm | 142.68212.33 kg/m | 189.57282.12 kg/m | +33% | -1% |
Bore, weight and flow area are derived from the published outside diameter and wall thickness. Weight is bare steel pipe: w = 10.6802 × t × (OD − t).
Why the old names persist
Because they are what the mills roll and what the warehouse stocks. In large diameter, STD and XS are the two walls most likely to be on the rack, so a designer who can live with 0.375 in gets material off the shelf instead of a mill run. The numbered schedules matter when the calculation demands a specific wall; the named ones matter when availability does.
Full tables: STD dimensions · XS dimensions · XS vs XXS · Sch 40 vs Sch 80.
Common questions
Is STD pipe the same as Schedule 40?
Through NPS 11, yes — identical walls. From NPS 12 upward STD stays at 0.375 in while Schedule 40 continues to thicken, so the two are different pipe in large bore.
Is XS the same as Schedule 80?
Through NPS 11, yes. From NPS 10 up, XS holds at 0.500 in and Schedule 80 keeps increasing, so they diverge one size earlier than STD and Schedule 40 do.
What does Extra Strong mean?
It is a wall designation, not a material or a grade. Extra Strong pipe is ordinary pipe with a heavier wall than Standard weight — the steel is whatever the material specification says it is.
Which is heavier, STD or XS?
XS, in every size — on average about 35% heavier than STD across the sizes that publish both.