Steel pipe schedule chart: sizes, wall and weight

Updated November 2, 2026  ·  Indumor

That a 2-inch pipe measures 2 inches is the first thing anyone assumes, and it is true nowhere. Outside it measures 60.3 mm, which is 2.375 inches. Inside, in SCH 40, 52.5 mm, about 2.07 inches. The number is a name, and it has to be read as a name.

The first table gives the dimensions from NPS 1/8 to 24 in the most used walls. The second adds the light schedules and the STD and XS weights of the large sizes. Both follow ASME B36.10M-2018, and the kilograms per meter come from its formula.

Steel pipe schedule chart: dimensions and weight

Large sizes: SCH 10, 20 and 30, STD and XS

The problem: one name for different pipes

NPS 2 sets the outside diameter and nothing else. The wall comes from the schedule, and the outside stays put so the same flanges, threads and fittings still work: when the wall grows, it grows inward. Those sizes come from the practice Robert Briggs set at the Pascal Iron Works in Philadelphia, which ASME adopted as a standard in 1886. Up to NPS 12, the outside diameter was chosen so that a pipe with the typical wall of the day had a bore close to its name. That link is long gone; from NPS 14 up, the outside diameter does match the number.

The schedule number is not a thickness either. SCH 40 is 3.91 mm at 2 inches and 8.18 mm at 8 inches. It arrived with the American standard of the 1930s, with the idea that it would track pressure and allowable stress. That could not be kept up, and it remained as a handy designation for ordering. Nor is XXS always the heaviest: from NPS 8 up, SCH 160 beats it. And DN 50 is the metric designation of NPS 2: another name, not a measurement.

The consequence: numbers and parts that do not add up

If an order simply says “2-inch pipe,” it can mean 5.44 kg/m in SCH 40 or 7.48 in SCH 80, almost 38 % more steel. And if a fitting from another schedule shows up on the line, the outsides match but the bores do not: that leaves a step at the weld root, and inspection will have something to say about it. Whoever sizes the flow is not off the hook either, because the bore of 2-inch SCH 160 is 42.8 mm against 52.5 for SCH 40.

The fix: order it by its full name

A complete order gives size, schedule, material and whether it is seamless or welded: “NPS 2, SCH 40, ASTM A106 grade B, seamless.” In Argentina, name the standard, because IRAM 2502, the general-purpose series for water, air and fire lines, is not SCH 40: at 2 inches it has a 3.25 mm wall instead of 3.91, and at 2 1/2, 5 and 6 inches even the outside diameter changes. That series is sold in 6.40 m lengths; seamless pipe usually comes in 12 m. If you need a wall that is not listed here, the weight comes from the standard's own formula:

kg/m = (OD − t) × t × 0.0246615

With OD and t in millimeters. For NPS 2 SCH 40: (60.3 − 3.91) × 3.91 × 0.0246615 = 5.44 kg/m. The formula is for carbon steel; stainless weighs 1 to 2 % more. For stainless, ASME B36.19 applies, with schedules 5S, 10S, 40S and 80S: 40S matches SCH 40 up to NPS 10 and 80S matches SCH 80 up to NPS 8, and beyond that they are thinner. These tables follow the 2018 edition of B36.10M; since 2022 the standard is called B36.10, without the M, and rounds some millimeters differently, so NPS 24 goes from 610 to 609.6 mm.

Further reading

• If the line can be built before it reaches the plant, continue with shop or field piping.
• Pipe racks: what those lines rest on.
• Inches to millimeters: the table for converting fractions.
• Industrial piping from Indumor, for when you want a quote on the prefabricated line.

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