XS vs XXS Pipe
Extra Strong against Double Extra Strong — the two heaviest named walls, and how much bore the second one costs you.
- Sizes with both
- 17 (NPS 1/2 – NPS 12)
- XXS weight penalty
- +78% on average
- Flow area lost
- -38% on average
- XXS wall
- Roughly twice XS in small bore
Short answer. Double Extra Strong is the heaviest wall in the traditional series — close to twice the XS wall in small bore. Across the 17 sizes that publish both, XXS adds 78% weight and gives up 38% of the flow area. It is specified for mechanical severity — erosion, impact, vibration — at least as often as for pressure.
The bore closes fast
At NPS 1/2 the XXS wall of 0.294 in (7.5 mm) leaves a bore of 0.252 in (6.4 mm) against the XS bore of 0.546 in (13.9 mm) — a flow area of 0.050 in² where XS gives 0.234 in². In the smallest sizes XXS is closer to heavy bar with a hole in it than to pipe, and it is used accordingly: as sample connections, as nipples on vibrating machinery, and as sacrificial wall in slurry and catalyst service.
Dimensions are given in inches, with the millimetre equivalent beneath in grey.
| NPS | OD | XS wall | XXS wall | XS bore | XXS bore | XS weight | XXS weight | Weight change | Flow area change |
|---|---|---|---|---|---|---|---|---|---|
| NPS 1/2 | 0.84021.34 mm | 0.1473.73 mm | 0.2947.47 mm | 0.54613.87 mm | 0.2526.40 mm | 1.091.62 kg/m | 1.712.55 kg/m | +58% | -79% |
| NPS 3/4 | 1.05026.67 mm | 0.1543.91 mm | 0.3087.82 mm | 0.74218.85 mm | 0.43411.02 mm | 1.472.19 kg/m | 2.443.63 kg/m | +66% | -66% |
| NPS 1 | 1.31533.40 mm | 0.1794.55 mm | 0.3589.09 mm | 0.95724.31 mm | 0.59915.21 mm | 2.173.23 kg/m | 3.665.45 kg/m | +68% | -61% |
| NPS 1 1/4 | 1.66042.16 mm | 0.1914.85 mm | 0.3829.70 mm | 1.27832.46 mm | 0.89622.76 mm | 3.004.46 kg/m | 5.217.76 kg/m | +74% | -51% |
| NPS 1 1/2 | 1.90048.26 mm | 0.2005.08 mm | 0.40010.16 mm | 1.50038.10 mm | 1.10027.94 mm | 3.635.40 kg/m | 6.419.54 kg/m | +76% | -46% |
| NPS 2 | 2.37560.32 mm | 0.2185.54 mm | 0.43611.07 mm | 1.93949.25 mm | 1.50338.18 mm | 5.027.47 kg/m | 9.0313.44 kg/m | +80% | -40% |
| NPS 2 1/2 | 2.87573.02 mm | 0.2767.01 mm | 0.55214.02 mm | 2.32359.00 mm | 1.77144.98 mm | 7.6611.40 kg/m | 13.7020.38 kg/m | +79% | -42% |
| NPS 3 | 3.50088.90 mm | 0.3007.62 mm | 0.60015.24 mm | 2.90073.66 mm | 2.30058.42 mm | 10.2515.26 kg/m | 18.5827.66 kg/m | +81% | -37% |
| NPS 3 1/2 | 4.000101.60 mm | 0.3188.08 mm | 0.63616.15 mm | 3.36485.45 mm | 2.72869.29 mm | 12.5118.61 kg/m | 22.8534.00 kg/m | +83% | -34% |
| NPS 4 | 4.500114.30 mm | 0.3378.56 mm | 0.67417.12 mm | 3.82697.18 mm | 3.15280.06 mm | 14.9822.30 kg/m | 27.5440.99 kg/m | +84% | -32% |
| NPS 4 1/2 | 5.000127.00 mm | 0.3559.02 mm | 0.71018.03 mm | 4.290108.97 mm | 3.58090.93 mm | 17.6126.21 kg/m | 32.5348.41 kg/m | +85% | -30% |
| NPS 5 | 5.563141.30 mm | 0.3759.52 mm | 0.75019.05 mm | 4.813122.25 mm | 4.063103.20 mm | 20.7830.92 kg/m | 38.5557.37 kg/m | +86% | -29% |
| NPS 6 | 6.625168.27 mm | 0.43210.97 mm | 0.86421.95 mm | 5.761146.33 mm | 4.897124.38 mm | 28.5742.52 kg/m | 53.1679.11 kg/m | +86% | -28% |
| NPS 7 | 7.625193.67 mm | 0.50012.70 mm | 0.87522.22 mm | 6.625168.27 mm | 5.875149.22 mm | 38.0556.62 kg/m | 63.0893.87 kg/m | +66% | -21% |
| NPS 8 | 8.625219.07 mm | 0.50012.70 mm | 0.87522.22 mm | 7.625193.67 mm | 6.875174.62 mm | 43.3964.57 kg/m | 72.43107.78 kg/m | +67% | -19% |
| NPS 10 | 10.750273.05 mm | 0.50012.70 mm | 1.00025.40 mm | 9.750247.65 mm | 8.750222.25 mm | 54.7481.46 kg/m | 104.13154.97 kg/m | +90% | -19% |
| NPS 12 | 12.750323.85 mm | 0.50012.70 mm | 1.00025.40 mm | 11.750298.45 mm | 10.750273.05 mm | 65.4297.35 kg/m | 125.49186.75 kg/m | +92% | -16% |
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).
XXS is not a schedule number
There is no Schedule 200. XXS is a named wall carried over from the wrought-iron era, and it does not line up neatly with the numbered series: in some sizes it is thicker than Schedule 160, in others thinner. Specify it by name and check the actual wall in the table rather than assuming it sits at the top of the schedule ladder.
Full tables: XS dimensions · XXS dimensions · Sch 40 vs Sch 160 · all schedules.
Common questions
Is XXS thicker than Schedule 160?
Not always. The two series were developed separately, so in some sizes XXS is the heavier wall and in others Schedule 160 is. Compare the published walls for the specific NPS.
What is XXS pipe used for?
Erosive and abrasive service, vibrating small-bore connections, high-pressure hydraulic lines, and anywhere a thick wall is wanted for mechanical robustness rather than hoop stress alone.
Is there anything heavier than XXS?
Not in the named series. Beyond XXS the wall is specified directly as a dimension, and the pipe is ordered to that thickness rather than to a schedule or a name.
Can XXS pipe be threaded?
Yes, and it is one of the reasons XXS nipples exist — there is ample wall left under the thread root, which is exactly what a thinner wall lacks.