Steel pipe sizes — ASME B36.10
Outside diameter is fixed per NPS and never matches the nominal name below NPS 14. The circumference column is for installed pipe you can only wrap a tape around: read the tape, find the row. Inside diameters shown for the two most common schedules; all values in mm unless marked.
| NPS | DN | OD (in) | OD | Circumf. | Sch 40 wall | Sch 40 ID | Sch 80 wall | Sch 80 ID |
|---|---|---|---|---|---|---|---|---|
| NPS 1/8 | 6 | 0.405″ | 10.29 | 32.3 | 1.73 | 6.83 | 2.41 | 5.46 |
| NPS 1/4 | 8 | 0.540″ | 13.72 | 43.1 | 2.24 | 9.25 | 3.02 | 7.67 |
| NPS 3/8 | 10 | 0.675″ | 17.14 | 53.9 | 2.31 | 12.52 | 3.20 | 10.74 |
| NPS 1/2 | 15 | 0.840″ | 21.34 | 67.0 | 2.77 | 15.80 | 3.73 | 13.87 |
| NPS 3/4 | 20 | 1.050″ | 26.67 | 83.8 | 2.87 | 20.93 | 3.91 | 18.85 |
| NPS 1 | 25 | 1.315″ | 33.40 | 104.9 | 3.38 | 26.64 | 4.55 | 24.31 |
| NPS 1-1/4 | 32 | 1.660″ | 42.16 | 132.5 | 3.56 | 35.05 | 4.85 | 32.46 |
| NPS 1-1/2 | 40 | 1.900″ | 48.26 | 151.6 | 3.68 | 40.89 | 5.08 | 38.10 |
| NPS 2 | 50 | 2.375″ | 60.32 | 189.5 | 3.91 | 52.50 | 5.54 | 49.25 |
| NPS 2-1/2 | 65 | 2.875″ | 73.02 | 229.4 | 5.16 | 62.71 | 7.01 | 59.00 |
| NPS 3 | 80 | 3.500″ | 88.90 | 279.3 | 5.49 | 77.93 | 7.62 | 73.66 |
| NPS 3-1/2 | 90 | 4.000″ | 101.60 | 319.2 | 5.74 | 90.12 | 8.08 | 85.45 |
| NPS 4 | 100 | 4.500″ | 114.30 | 359.1 | 6.02 | 102.26 | 8.56 | 97.18 |
| NPS 5 | 125 | 5.563″ | 141.30 | 443.9 | 6.55 | 128.19 | 9.52 | 122.25 |
| NPS 6 | 150 | 6.625″ | 168.27 | 528.7 | 7.11 | 154.05 | 10.97 | 146.33 |
| NPS 8 | 200 | 8.625″ | 219.07 | 688.2 | 8.18 | 202.72 | 12.70 | 193.67 |
| NPS 10 | 250 | 10.750″ | 273.05 | 857.8 | 9.27 | 254.51 | 15.09 | 242.87 |
| NPS 12 | 300 | 12.750″ | 323.85 | 1017.4 | 10.31 | 303.23 | 17.48 | 288.90 |
| NPS 14 | 350 | 14.000″ | 355.60 | 1117.2 | 11.13 | 333.35 | 19.05 | 317.50 |
| NPS 16 | 400 | 16.000″ | 406.40 | 1276.7 | 12.70 | 381.00 | 21.44 | 363.52 |
| NPS 18 | 450 | 18.000″ | 457.20 | 1436.3 | 14.27 | 428.65 | 23.83 | 409.55 |
| NPS 20 | 500 | 20.000″ | 508.00 | 1595.9 | 15.09 | 477.82 | 26.19 | 455.63 |
| NPS 24 | 600 | 24.000″ | 609.60 | 1915.1 | 17.48 | 574.65 | 30.96 | 547.67 |
From NPS 14 up, OD equals the nominal size in inches. Walls per ASME B36.10M; other schedules (5, 10, 160, STD, XS, XXS) exist — measure the wall at a cut end or consult the full standard when it matters structurally.