Nominal pipe sizes
31 sizes, 367 tabulated size-and-schedule combinations. The outside diameter is fixed per size and the wall varies with schedule — so this table tells you the diameter, and the per-size pages tell you what fits on it.
| Nominal size | Metric size | Outside dia. mm | in | Schedules | Sch 40 wall mm | Sch 40 bore mm | Sch 40 mass kg/m | lb/ft |
|---|---|---|---|---|---|---|---|---|
| NPS 1/8 | DN 6 | 10.3 | 0.405 | 10 | 1.73 | 6.8 | 0.365 | 0.245 |
| NPS 1/4 | DN 8 | 13.7 | 0.540 | 10 | 2.24 | 9.2 | 0.633 | 0.425 |
| NPS 3/8 | DN 10 | 17.1 | 0.675 | 10 | 2.31 | 12.5 | 0.846 | 0.568 |
| NPS 1/2 | DN 15 | 21.3 | 0.840 | 12 | 2.77 | 15.8 | 1.268 | 0.852 |
| NPS 3/4 | DN 20 | 26.7 | 1.050 | 12 | 2.87 | 20.9 | 1.685 | 1.132 |
| NPS 1 | DN 25 | 33.4 | 1.315 | 12 | 3.38 | 26.6 | 2.501 | 1.681 |
| NPS 1-1/4 | DN 32 | 42.2 | 1.660 | 12 | 3.56 | 35.1 | 3.386 | 2.275 |
| NPS 1-1/2 | DN 40 | 48.3 | 1.900 | 12 | 3.68 | 40.9 | 4.049 | 2.721 |
| NPS 2 | DN 50 | 60.3 | 2.375 | 12 | 3.91 | 52.5 | 5.442 | 3.657 |
| NPS 2-1/2 | DN 65 | 73.0 | 2.875 | 13 | 5.16 | 62.7 | 8.630 | 5.799 |
| NPS 3 | DN 80 | 88.9 | 3.500 | 13 | 5.49 | 77.9 | 11.286 | 7.584 |
| NPS 3-1/2 | DN 90 | 101.6 | 4.000 | 11 | 5.74 | 90.1 | 13.571 | 9.119 |
| NPS 4 | DN 100 | 114.3 | 4.500 | 13 | 6.02 | 102.3 | 16.075 | 10.802 |
| NPS 4-1/2 | DN 115 | 127.0 | 5.000 | 7 | 6.27 | 114.5 | 18.679 | 12.552 |
| NPS 5 | DN 125 | 141.3 | 5.563 | 12 | 6.55 | 128.2 | 21.777 | 14.633 |
| NPS 6 | DN 150 | 168.3 | 6.625 | 12 | 7.11 | 154.1 | 28.267 | 18.994 |
| NPS 8 | DN 200 | 219.1 | 8.625 | 17 | 8.18 | 202.7 | 42.538 | 28.584 |
| NPS 10 | DN 250 | 273.1 | 10.750 | 16 | 9.27 | 254.5 | 60.310 | 40.526 |
| NPS 12 | DN 300 | 323.8 | 12.750 | 16 | 10.31 | 303.2 | 79.739 | 53.582 |
| NPS 14 | DN 350 | 355.6 | 14.000 | 16 | 11.10 | 333.4 | 94.303 | 63.368 |
| NPS 16 | DN 400 | 406.4 | 16.000 | 16 | 12.70 | 381.0 | 123.307 | 82.859 |
| NPS 18 | DN 450 | 457.2 | 18.000 | 16 | 14.27 | 428.7 | 155.927 | 104.778 |
| NPS 20 | DN 500 | 508.0 | 20.000 | 16 | 15.06 | 477.9 | 183.105 | 123.041 |
| NPS 22 | DN 550 | 558.8 | 22.000 | 15 | — | — | — | — |
| NPS 24 | DN 600 | 609.6 | 24.000 | 16 | 17.45 | 574.7 | 254.825 | 171.234 |
| NPS 26 | DN 650 | 660.4 | 26.000 | 5 | — | — | — | — |
| NPS 28 | DN 700 | 711.2 | 28.000 | 6 | — | — | — | — |
| NPS 30 | DN 750 | 762.0 | 30.000 | 8 | — | — | — | — |
| NPS 32 | DN 800 | 812.8 | 32.000 | 7 | 17.48 | 777.8 | 342.757 | 230.322 |
| NPS 34 | DN 850 | 863.6 | 34.000 | 7 | 17.48 | 828.6 | 364.650 | 245.033 |
| NPS 36 | DN 900 | 914.4 | 36.000 | 7 | 19.05 | 876.3 | 420.637 | 282.655 |
Outside diameter in inches is the standard's governed value; the millimetre figure is that value × 25.4, displayed rounded. Schedule 40 is not tabulated above NPS 24, which is why the last rows show a dash. Mass is carbon steel at 7,850 kg/m³.
Open a size for its full cross-schedule table:
Why the diameters jump the way they do
The series looks arbitrary because it is historical rather than designed. For NPS 1/8 through NPS 12 the outside diameters are a legacy of iron pipe wall thicknesses chosen in the nineteenth century, so they step by fractions of an inch that do not follow a simple progression. From NPS 14 upward the series becomes a clean two-inch progression — 14, 16, 18, 20, 22, 24, then 30, 32, 34, 36 — because by then the sizes were defined rather than inherited.
Because outside diameter is fixed per size, a flange, a fitting or a thread gauges the same regardless of wall — so a size and a schedule can be chosen independently upstream of the fitting. That is the entire reason the convention survived. The cost is that the nominal size carries no dimensional information, and any calculation that needs a bore (flow, volume, weight) must consult the schedule as well. Everything on this site that reports a bore, internal volume or mass therefore states the schedule alongside it.
Sizes that exist in one system and not the other
The DN and NPS series are not one-to-one at the edges. NPS 4-1/2 (DN 115) and NPS 22 (DN 550) are real sizes with limited availability, and DN 6, 8 and 10 correspond to NPS 1/8, 1/4 and 3/8, which the metric system never uses in practice. If a drawing specifies one system and a supplier quotes the other, that is where the mismatch shows up.
Pipe reference and tools
Sizes are one axis; schedules are the other.
- Pipe overview — schedules, sizes and how weight is computed
- All pipe schedules — Sch 5S to XXS
- All nominal sizes — NPS 1/8 to NPS 36
- DN to NPS conversion — metric to imperial designations
- Pipe weight formula — worked derivation
- Pipe weight calculator — any OD and wall
- All calculators — metal weight and pipe weight
- Download the data — CSV, generated from the same source
- Cross-reference tables — DN / NPS / material equivalents
- Methodology and sources — where every number comes from
Outside diameters are the ASME B36.10M values in inches, converted at exactly 25.4 mm per inch. The Schedule 40 wall, bore and mass columns are computed here. DN values are the standard metric designations, not a conversion of the outside diameter.
- ASME B36.10M — Welded and Seamless Wrought Steel Pipe (dimensional tables).
- BIPM / NIST definitional constants: international inch = 25.4 mm, foot = 0.3048 m, pound = 0.45359237 kg.
Dataset version 2026.09.1 · dimensions last verified against source 2026-09-21. Found an error? Report it — corrections are issued with a version bump.