Find a pipe’s inside diameter
NPS 2 · DN 50 · Schedule 40
Nominal ID = OD − 2 × wall thickness.
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Pipe dimension table
Schedule 40 across nominal sizes
| NPS | DN | Wall series | OD (in / mm) | Wall (in / mm) | Calculated ID (in / mm) |
|---|---|---|---|---|---|
| 1/8 | 6 | Schedule 40 | 0.405 in / 10.29 mm | 0.068 in / 1.73 mm | 0.269 in / 6.83 mm |
| 1/4 | 8 | Schedule 40 | 0.540 in / 13.72 mm | 0.088 in / 2.24 mm | 0.364 in / 9.25 mm |
| 3/8 | 10 | Schedule 40 | 0.675 in / 17.14 mm | 0.091 in / 2.31 mm | 0.493 in / 12.52 mm |
| 1/2 | 15 | Schedule 40 | 0.840 in / 21.34 mm | 0.109 in / 2.77 mm | 0.622 in / 15.80 mm |
| 3/4 | 20 | Schedule 40 | 1.050 in / 26.67 mm | 0.113 in / 2.87 mm | 0.824 in / 20.93 mm |
| 1 | 25 | Schedule 40 | 1.315 in / 33.40 mm | 0.133 in / 3.38 mm | 1.049 in / 26.64 mm |
| 1 1/4 | 32 | Schedule 40 | 1.660 in / 42.16 mm | 0.140 in / 3.56 mm | 1.380 in / 35.05 mm |
| 1 1/2 | 40 | Schedule 40 | 1.900 in / 48.26 mm | 0.145 in / 3.68 mm | 1.610 in / 40.89 mm |
| 2 | 50 | Schedule 40 | 2.375 in / 60.32 mm | 0.154 in / 3.91 mm | 2.067 in / 52.50 mm |
| 2 1/2 | 65 | Schedule 40 | 2.875 in / 73.02 mm | 0.203 in / 5.16 mm | 2.469 in / 62.71 mm |
| 3 | 80 | Schedule 40 | 3.500 in / 88.90 mm | 0.216 in / 5.49 mm | 3.068 in / 77.93 mm |
| 3 1/2 | 90 | Schedule 40 | 4.000 in / 101.60 mm | 0.226 in / 5.74 mm | 3.548 in / 90.12 mm |
| 4 | 100 | Schedule 40 | 4.500 in / 114.30 mm | 0.237 in / 6.02 mm | 4.026 in / 102.26 mm |
| 5 | 125 | Schedule 40 | 5.563 in / 141.30 mm | 0.258 in / 6.55 mm | 5.047 in / 128.19 mm |
| 6 | 150 | Schedule 40 | 6.625 in / 168.27 mm | 0.280 in / 7.11 mm | 6.065 in / 154.05 mm |
| 8 | 200 | Schedule 40 | 8.625 in / 219.07 mm | 0.322 in / 8.18 mm | 7.981 in / 202.72 mm |
| 10 | 250 | Schedule 40 | 10.750 in / 273.05 mm | 0.365 in / 9.27 mm | 10.020 in / 254.51 mm |
| 12 | 300 | Schedule 40 | 12.750 in / 323.85 mm | 0.406 in / 10.31 mm | 11.938 in / 303.23 mm |
| 14 | 350 | Schedule 40 | 14.000 in / 355.60 mm | 0.438 in / 11.13 mm | 13.124 in / 333.35 mm |
| 16 | 400 | Schedule 40 | 16.000 in / 406.40 mm | 0.500 in / 12.70 mm | 15.000 in / 381.00 mm |
| 18 | 450 | Schedule 40 | 18.000 in / 457.20 mm | 0.562 in / 14.27 mm | 16.876 in / 428.65 mm |
| 20 | 500 | Schedule 40 | 20.000 in / 508.00 mm | 0.594 in / 15.09 mm | 18.812 in / 477.82 mm |
| 22 | 550 | Schedule 40 | 22.000 in / 558.80 mm | — | Not tabulated |
| 24 | 600 | Schedule 40 | 24.000 in / 609.60 mm | 0.688 in / 17.48 mm | 22.624 in / 574.65 mm |
No matching rows. Clear the size filter or change the comparison.
A dash means the combination is not provided in this reference’s source grid. It is not a zero wall and does not establish whether a supplier can manufacture it. The table covers 24 common nominal sizes from NPS 1/8 through 24, with 314 tabulated combinations across 17 wall series.
NPS, DN, schedule, and ID explained
NPS and DN are nominal size designations. Neither should be entered directly as an inside diameter. A 2-inch Schedule 40 steel pipe has a 2.375-inch OD and 2.067-inch nominal ID.
Schedule identifies a wall series. For a given NPS, OD stays fixed while different walls change the bore. A larger schedule commonly means a thicker wall, but use the actual table entry. A schedule alone is not a pressure rating.
Use ID for flow and OD for insulation. Pressure drop, velocity, Reynolds number, and relative roughness depend on the internal flow passage. Pipe insulation calculations start at the outside surface. Orifice bores and venturi throats are separate dimensions, not pipe schedule IDs.
The dimension series here concern steel and stainless steel pipe. Do not assume they describe copper tubing, sanitary tubing, ductwork, cast iron, PVC/CPVC, or HDPE. Use the product specification for those systems.
Schedule 40 versus 40S, and STD versus XS
| Comparison | Where listed dimensions match | Example where they differ |
|---|---|---|
| 40, 40S, and STD | Through NPS 10 in this table | NPS 12: 40 wall = 0.406 in; 40S / STD = 0.375 in |
| 80, 80S, and XS | Through NPS 8 in this table | NPS 10: 80 wall = 0.594 in; 80S / XS = 0.500 in |
| 10 and 10S | Through NPS 12 in this table | NPS 14: 10 wall = 0.250 in; 10S = 0.188 in |
The “S” designation belongs to the stainless dimensional series. Verify the specified series, especially for larger sizes. STD = standard weight; XS = extra strong; XXS = double extra strong. XXS is not another name for Schedule 160.
Nominal dimensions and actual pipe
The calculation is ID = OD − 2t, with flow area A = πID²/4. Manufacturing tolerances, lining, deposits, corrosion, and weld details can change the actual clear bore. Use measured or vendor-certified dimensions when required by the calculation.
Inch dimensions are used for the displayed ID calculation; millimeters are converted using exactly 25.4 mm/in. Published metric tables use rounded nominal dimensions and can differ slightly. Where the inch thickness is not tabulated by Tioga, the Atlas metric thickness is converted and rounded to 0.001 inch.
For pressure design, check the applicable piping code, material, temperature, allowances, and tolerances. This lookup does not establish allowable pressure.
Sources
- Atlas Steels, Technical Note 12, Pipe Dimensions, revised April 8, 2021, page 4: source schedule grid, NPS/DN sizes, and nominal wall dimensions. The note identifies its B36.10M/B36.19M dimensional basis.
- Tioga, Pipe Dimensions and Weights: published inch OD/wall dimensions and cross-checks. IDs on this page are calculated from dimensions rather than copied from rounded supplier ID columns.