Stainless Steel Pipe Size Chart: NPS, DN, OD & Schedule
How pipe sizing actually works — why the outside diameter is fixed and the wall changes with schedule — plus verified NPS/DN/OD and SCH 5S/10S/40S/80S charts in mm per ASME B36.19M, and the weight formula.
NPS, DN, OD and schedule — what each one means
Stainless pipe is specified by two things: a size designation (which fixes the outside diameter) and a schedule (which fixes the wall thickness). Getting these two right is all you need to fully describe a pipe's cross-section.
The reason NPS 1/8 to 12 don't match their OD is historical: these sizes were originally chosen to give a target inside diameter at the wall thicknesses common at the time. As wall options multiplied, the ID drifted and NPS became only an indirect label. From NPS 14 up, NPS equals the OD in inches exactly.
NPS / DN / OD chart (mm and inches)
The outside diameter for each size is constant regardless of schedule. Values are the nominal outside diameters per ASME B36.19M (which align with ASME B36.10M for the same NPS).
| NPS | DN | OD (mm) | OD (in) |
|---|---|---|---|
| 1/8 | 6 | 10.29 | 0.405 |
| 1/4 | 8 | 13.72 | 0.540 |
| 3/8 | 10 | 17.15 | 0.675 |
| 1/2 | 15 | 21.34 | 0.840 |
| 3/4 | 20 | 26.67 | 1.050 |
| 1 | 25 | 33.40 | 1.315 |
| 1-1/4 | 32 | 42.16 | 1.660 |
| 1-1/2 | 40 | 48.26 | 1.900 |
| 2 | 50 | 60.33 | 2.375 |
| 2-1/2 | 65 | 73.03 | 2.875 |
| 3 | 80 | 88.90 | 3.500 |
| 4 | 100 | 114.30 | 4.500 |
| 6 | 150 | 168.28 | 6.625 |
| 8 | 200 | 219.08 | 8.625 |
| 10 | 250 | 273.05 | 10.750 |
| 12 | 300 | 323.85 | 12.750 |
Schedule wall thickness (mm) — 5S / 10S / 40S / 80S
Wall thickness in millimetres for the four stainless schedules, per ASME B36.19M. A dash means the schedule is not defined for that size. For most sizes 40S equals Standard (STD) wall and 80S equals Extra-Strong (XS).
| NPS | DN | OD (mm) | SCH 5S | SCH 10S | SCH 40S | SCH 80S |
|---|---|---|---|---|---|---|
| 1/8 | 6 | 10.29 | — | 1.24 | 1.73 | 2.41 |
| 1/4 | 8 | 13.72 | — | 1.65 | 2.24 | 3.02 |
| 3/8 | 10 | 17.15 | — | 1.65 | 2.31 | 3.20 |
| 1/2 | 15 | 21.34 | 1.65 | 2.11 | 2.77 | 3.73 |
| 3/4 | 20 | 26.67 | 1.65 | 2.11 | 2.87 | 3.91 |
| 1 | 25 | 33.40 | 1.65 | 2.77 | 3.38 | 4.55 |
| 1-1/4 | 32 | 42.16 | 1.65 | 2.77 | 3.56 | 4.85 |
| 1-1/2 | 40 | 48.26 | 1.65 | 2.77 | 3.68 | 5.08 |
| 2 | 50 | 60.33 | 1.65 | 2.77 | 3.91 | 5.54 |
| 2-1/2 | 65 | 73.03 | 2.11 | 3.05 | 5.16 | 7.01 |
| 3 | 80 | 88.90 | 2.11 | 3.05 | 5.49 | 7.62 |
| 4 | 100 | 114.30 | 2.11 | 3.05 | 6.02 | 8.56 |
| 6 | 150 | 168.28 | 2.77 | 3.40 | 7.11 | 10.97 |
| 8 | 200 | 219.08 | 2.77 | 3.76 | 8.18 | 12.70 |
| 10 | 250 | 273.05 | 3.40 | 4.19 | 9.27 | 12.70 |
| 12 | 300 | 323.85 | 3.96 | 4.57 | 9.53 | 12.70 |
Pipe weight formula (kg per metre)
Once you know the OD and wall thickness, the theoretical weight of a length of austenitic stainless pipe follows directly from the cross-sectional area of the metal ring and the density.
Worked example
NPS 2, Schedule 40S: OD = 60.33 mm, WT = 3.91 mm.
This is a theoretical plain-end weight. Real bundles vary with tolerance, weld bead (on welded pipe) and end finishing, so use it for estimating freight and quantities, not for billing weight. Note that published mill / ASME B36.19M plain-end weight tables list NPS 2 SCH 40S at about 5.44 kg/m; the small difference comes from the slightly lower density basis used in those legacy tables, and either value is acceptable for estimating.
Pipe (NPS) vs tube (OD) — don't mix them up
The single most common ordering error is confusing pipe and tube sizing:
If a drawing calls for "1 inch", ask whether it means NPS 1 pipe (33.4 mm OD) or 1 inch (25.4 mm OD) tube — they are different parts. See our stainless steel pipe & tube standards hub for which standard covers which product, and mechanical & structural tube when you need OD-based tube.
FAQ
Why isn't the outside diameter the same as the pipe size (NPS)?
For NPS 1/8 to 12, NPS is a nominal label rather than a measurement — the sizes were originally set to give a target inside diameter at the wall thicknesses common at the time. So NPS 1 pipe actually has a 33.40 mm OD, and NPS 2 is 60.33 mm. From NPS 14 upward, the NPS number does equal the OD in inches.
What is the difference between schedule 10S, 40S and 80S?
Schedule is a code for wall thickness at a given size: the higher the number, the thicker the wall and the higher the pressure rating. The OD stays fixed, so a thicker schedule eats into the bore. For NPS 2 the wall is 2.77 mm at 10S, 3.91 mm at 40S and 5.54 mm at 80S per ASME B36.19M. The "S" suffix marks the stainless wall series.
How do I calculate stainless steel pipe weight per metre?
Use kg/m = (OD − WT) × WT × 0.02491, with OD and WT in mm. The 0.02491 constant is for 304-type stainless at about 7.93 g/cm³; for 316/316L multiply by roughly 1.006. Example: NPS 2 SCH 40S (OD 60.33, WT 3.91) gives about 5.49 kg/m. It is a theoretical plain-end weight, so allow for tolerance.
What is the difference between pipe and tube sizing?
Pipe is ordered by NPS/DN plus a schedule, and its label usually does not equal the OD. Tube is ordered by exact outside diameter plus wall thickness, so a 25 mm tube really measures 25 mm OD. When a drawing just says "1 inch", confirm whether it means NPS 1 pipe (33.4 mm OD) or 1 inch tube (25.4 mm OD) before ordering.
Pipe, tube & reference pages
Need a specific size, schedule or wall?
Manufacturer-direct from Foshan since 2006. Send us NPS + schedule or OD + wall and we'll confirm dimensions, grade and finish against stock.