Pipe schedule chart: wall thickness, OD and ID by NPS (mm and inches)
Deskely Completions team Singapore
A pipe schedule sets the wall thickness of a pipe for each nominal size. Schedule 40 on a 2 inch pipe and schedule 40 on a 12 inch pipe are different thicknesses, so the schedule only means something together with the size. This chart gives the outside diameter and wall thickness of steel pipe from 1/8 to 24 inch, by schedule, in mm and inches.
The dimensions follow ASME B36.10M for welded and seamless wrought steel pipe and ASME B36.19M for stainless steel pipe (the S schedules). Choose a size and schedule to get the inside diameter and the weight per metre.
- NPS is a name, not a measurement: from 14 inch up the outside diameter equals the NPS; below it, it does not.
- For one NPS the outside diameter is fixed. A heavier schedule makes the wall thicker and the bore smaller.
- STD, XS and XXS are weight classes. STD equals schedule 40 up to 10 inch, and XS equals schedule 80 up to 8 inch.
- Schedules with an S, such as 10S and 40S, are the stainless steel schedules of ASME B36.19M.
Pipe schedule chart
Click a row to look up a size. Blank cells are sizes where that schedule is not listed here.
- Outside diameter
- 114.3 mm
- Wall thickness
- 6.02 mm
- Inside diameter
- 102.26 mm
- Weight, carbon steel
- 16.08 kg/m
Weight = 0.0246615 x (OD - t) x t kg/m, for carbon steel. Stainless steel is about 2 percent heavier.
| NPS | OD | 5S | 10S | 10 | 20 | 30 | STD | 40 | 60 | XS | 80 | 100 | 120 | 140 | 160 | XXS |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1/8 | 10.3 | 1.24 | 1.73 | 1.73 | 2.41 | 2.41 | ||||||||||
| 1/4 | 13.7 | 1.65 | 2.24 | 2.24 | 3.02 | 3.02 | ||||||||||
| 3/8 | 17.1 | 1.65 | 2.31 | 2.31 | 3.20 | 3.20 | ||||||||||
| 1/2 | 21.3 | 1.65 | 2.11 | 2.11 | 2.41 | 2.77 | 2.77 | 3.73 | 3.73 | 4.78 | 7.47 | |||||
| 3/4 | 26.7 | 1.65 | 2.11 | 2.11 | 2.41 | 2.87 | 2.87 | 3.91 | 3.91 | 5.56 | 7.82 | |||||
| 1 | 33.4 | 1.65 | 2.77 | 2.77 | 2.90 | 3.38 | 3.38 | 4.55 | 4.55 | 6.35 | 9.09 | |||||
| 1-1/4 | 42.2 | 1.65 | 2.77 | 2.77 | 2.97 | 3.56 | 3.56 | 4.85 | 4.85 | 6.35 | 9.70 | |||||
| 1-1/2 | 48.3 | 1.65 | 2.77 | 2.77 | 3.18 | 3.68 | 3.68 | 5.08 | 5.08 | 7.14 | 10.15 | |||||
| 2 | 60.3 | 1.65 | 2.77 | 2.77 | 3.18 | 3.91 | 3.91 | 5.54 | 5.54 | 8.74 | 11.07 | |||||
| 2-1/2 | 73 | 2.11 | 3.05 | 5.16 | 5.16 | 7.01 | 7.01 | 9.53 | 14.02 | |||||||
| 3 | 88.9 | 2.11 | 3.05 | 5.49 | 5.49 | 7.62 | 7.62 | 11.13 | 15.24 | |||||||
| 3-1/2 | 101.6 | 2.11 | 3.05 | 5.74 | 5.74 | 8.08 | 8.08 | |||||||||
| 4 | 114.3 | 2.11 | 3.05 | 6.02 | 6.02 | 8.56 | 8.56 | 11.13 | 13.49 | 17.12 | ||||||
| 5 | 141.3 | 2.77 | 3.40 | 6.55 | 6.55 | 9.53 | 9.53 | 12.70 | 15.88 | 19.05 | ||||||
| 6 | 168.3 | 2.77 | 3.40 | 7.11 | 7.11 | 10.97 | 10.97 | 14.27 | 18.26 | 21.95 | ||||||
| 8 | 219.1 | 2.77 | 3.76 | 6.35 | 7.04 | 8.18 | 8.18 | 10.31 | 12.70 | 12.70 | 15.09 | 18.26 | 20.62 | 23.01 | 22.23 | |
| 10 | 273.1 | 3.40 | 4.19 | 6.35 | 7.80 | 9.27 | 9.27 | 12.70 | 12.70 | 15.09 | 18.26 | 21.44 | 25.40 | 28.58 | 25.40 | |
| 12 | 323.8 | 3.96 | 4.57 | 6.35 | 8.38 | 9.53 | 10.31 | 14.27 | 12.70 | 17.48 | 21.44 | 25.40 | 28.58 | 33.32 | 25.40 | |
| 14 | 355.6 | 3.96 | 4.78 | 6.35 | 7.92 | 9.53 | 9.53 | 11.13 | 15.09 | 12.70 | 19.05 | 23.83 | 27.79 | 31.75 | 35.71 | |
| 16 | 406.4 | 4.19 | 4.78 | 6.35 | 7.92 | 9.53 | 9.53 | 12.70 | 16.66 | 12.70 | 21.44 | 26.19 | 30.96 | 36.53 | 40.49 | |
| 18 | 457 | 4.19 | 4.78 | 6.35 | 7.92 | 11.13 | 9.53 | 14.27 | 19.05 | 12.70 | 23.83 | 29.36 | 34.93 | 39.67 | 45.24 | |
| 20 | 508 | 4.78 | 5.54 | 6.35 | 9.53 | 12.70 | 9.53 | 15.09 | 20.62 | 12.70 | 26.19 | 32.54 | 38.10 | 44.45 | 50.01 | |
| 24 | 610 | 5.54 | 6.35 | 6.35 | 9.53 | 14.27 | 9.53 | 17.48 | 24.61 | 12.70 | 30.96 | 38.89 | 46.02 | 52.37 | 59.54 |
Line sizes and tags read from your drawings into a register: Deskely Extract
Dimensions in this chart are nominal. Mill tolerances apply, and the pipe specification and purchase order for your project take precedence.
NPS, DN and outside diameter
NPS (nominal pipe size) is the North American size designation, in inches. DN (diameter nominal) is the metric equivalent: NPS 2 is DN 50, NPS 4 is DN 100. Neither is an actual measurement.
What is fixed for each NPS is the outside diameter, so that fittings and flanges fit any schedule of that size. From NPS 14 up, the outside diameter in inches equals the NPS; below NPS 14 it is larger, for example 2.375 inches (60.3 mm) for NPS 2.
Schedules and weight classes
- Numbered schedules (5, 10, 20, 30, 40, 60, 80, 100, 120, 140, 160) come from ASME B36.10M. The higher the number, the thicker the wall.
- Weight classes STD (standard), XS (extra strong) and XXS (double extra strong) are the older designations, still widely used.
- S schedules (5S, 10S, 40S, 80S) come from ASME B36.19M for stainless steel. 40S and 80S match STD and XS up to 12 inch.
STD and schedule 40 are the same up to NPS 10, then STD stays at 9.53 mm while schedule 40 keeps growing. XS and schedule 80 are the same up to NPS 8, then XS stays at 12.70 mm.
Schedule 40 pipe dimensions
Schedule 40 is the most common schedule for steel process and utility piping. Its dimensions for every size, with the inside diameter and the weight per metre of carbon steel pipe:
| NPS | OD mm (in) | Wall mm (in) | ID mm (in) | kg/m |
|---|---|---|---|---|
| 1/8 | 10.3 (0.405) | 1.73 (0.068) | 6.8 (0.269) | 0.37 |
| 1/4 | 13.7 (0.540) | 2.24 (0.088) | 9.2 (0.363) | 0.63 |
| 3/8 | 17.1 (0.675) | 2.31 (0.091) | 12.5 (0.491) | 0.84 |
| 1/2 | 21.3 (0.840) | 2.77 (0.109) | 15.8 (0.620) | 1.27 |
| 3/4 | 26.7 (1.050) | 2.87 (0.113) | 21.0 (0.825) | 1.69 |
| 1 | 33.4 (1.315) | 3.38 (0.133) | 26.6 (1.049) | 2.50 |
| 1-1/4 | 42.2 (1.660) | 3.56 (0.140) | 35.1 (1.381) | 3.39 |
| 1-1/2 | 48.3 (1.900) | 3.68 (0.145) | 40.9 (1.612) | 4.05 |
| 2 | 60.3 (2.375) | 3.91 (0.154) | 52.5 (2.066) | 5.44 |
| 2-1/2 | 73 (2.875) | 5.16 (0.203) | 62.7 (2.468) | 8.63 |
| 3 | 88.9 (3.500) | 5.49 (0.216) | 77.9 (3.068) | 11.29 |
| 3-1/2 | 101.6 (4.000) | 5.74 (0.226) | 90.1 (3.548) | 13.57 |
| 4 | 114.3 (4.500) | 6.02 (0.237) | 102.3 (4.026) | 16.08 |
| 5 | 141.3 (5.563) | 6.55 (0.258) | 128.2 (5.047) | 21.77 |
| 6 | 168.3 (6.625) | 7.11 (0.280) | 154.1 (6.066) | 28.26 |
| 8 | 219.1 (8.625) | 8.18 (0.322) | 202.7 (7.982) | 42.55 |
| 10 | 273.1 (10.750) | 9.27 (0.365) | 254.6 (10.022) | 60.31 |
| 12 | 323.8 (12.750) | 10.31 (0.406) | 303.2 (11.936) | 79.71 |
| 14 | 355.6 (14.000) | 11.13 (0.438) | 333.3 (13.124) | 94.55 |
| 16 | 406.4 (16.000) | 12.70 (0.500) | 381.0 (15.000) | 123.31 |
| 18 | 457 (18.000) | 14.27 (0.562) | 428.5 (16.869) | 155.81 |
| 20 | 508 (20.000) | 15.09 (0.594) | 477.8 (18.812) | 183.43 |
| 24 | 610 (24.000) | 17.48 (0.688) | 575.0 (22.639) | 255.43 |
Up to NPS 10, schedule 40 and STD are the same wall. From NPS 12 up, schedule 40 is thicker than STD. For stainless steel pipe, 40S has the same wall as schedule 40 up to NPS 10.
Inside diameter and weight
The inside diameter is the outside diameter minus twice the wall thickness. The weight of plain-end carbon steel pipe per metre is:
W (kg/m) = 0.0246615 x (OD - t) x t, with OD and wall thickness t in mm. For a 4 inch schedule 40 pipe: 0.0246615 x (114.3 - 6.02) x 6.02 = 16.08 kg/m.
Stainless steel is slightly denser, so its weight is about 2 percent higher.
How the schedule is chosen
The schedule is set by the piping class in the project piping specification. The piping engineer works out the minimum wall thickness for the design pressure and temperature, the material and the corrosion allowance, using the design code (ASME B31.3 for process piping), and picks the next schedule up that meets it after mill tolerance. The schedule then shows up on the line list, the P&ID line number, the isometric and the bill of materials.
On site, the wall thickness of the installed pipe is one of the checks behind the pressure test. See the hydrostatic test guide and the piping isometric symbols.
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Frequently asked questions
What is a pipe schedule?
A designation for the wall thickness of a pipe at a given nominal size. For each size, a higher schedule number means a thicker wall and a smaller bore, with the same outside diameter.
What is the wall thickness of schedule 40 pipe?
It depends on the size: 2.77 mm for 1/2 inch, 3.91 mm for 2 inch, 6.02 mm for 4 inch, 8.18 mm for 8 inch and 10.31 mm for 12 inch. See the chart for every size.
What is the difference between schedule 40 and schedule 80?
Schedule 80 has a thicker wall than schedule 40 at the same size, so it is stronger and heavier, with a smaller inside diameter. The outside diameter is the same.
Is schedule 40 the same as STD?
Up to NPS 10, yes. From NPS 12 up, STD stays at 9.53 mm while schedule 40 is thicker.
What does the S in 40S mean?
It marks the stainless steel schedules of ASME B36.19M. 40S and 80S match STD and XS up to 12 inch.
Is NPS the same as the outside diameter?
Only from NPS 14 up. Below that the outside diameter is larger than the NPS, for example 60.3 mm (2.375 inch) for NPS 2.
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