NPS 1/8 stainless outer diameter: 0.405 in / 10.287 mm
- OD (inches)
- 0.405 in
- OD (millimetres)
- 10.287 mm
- DN
- 6
- Wall range
- 0.049–0.095 in
- Bore range
- 0.215–0.307 in
Stainless wrought pipe. Shares the B36.10 ODs; walls carry an S suffix (5S, 10S, 40S, 80S). For NPS 1/8, ASME B36.19M fixes the outside at 0.405 in / 10.287 mm; the 3 published wall series below are what change the bore.
| Wall series | Wall (in) | Wall (mm) | ID (in) | ID (mm) | Bore is | ≈ kg/m |
|---|---|---|---|---|---|---|
| Sch 10S | 0.049 | 1.245 | 0.307 | 7.798 | exact | 0.28 |
| Sch 40S | 0.068 | 1.727 | 0.269 | 6.833 | exact | 0.37 |
| Sch 80S | 0.095 | 2.413 | 0.215 | 5.461 | exact | 0.47 |
Same body, different material. steel 1/8 Sch 40 = STD, and stainless 1/8 Sch 40S are the same 0.068 in wall on the same 0.405 in / 10.287 mm body; steel 1/8 Sch 80 = XS, and stainless 1/8 Sch 80S are the same 0.095 in wall on the same 0.405 in / 10.287 mm body. A caliper cannot separate them — what the pipe is made of does.
The same nominal label in other standards
| Standard | OD (in) | OD (mm) | DN | Published wall series |
|---|---|---|---|---|
| ASME B36.10M · welded and seamless steel pipe | 0.405 | 10.287 | 6 | Sch 40 0.068 · Sch 80 0.095 · STD 0.068 · XS 0.095 |
| ASME B36.19M · stainless steel pipe | 0.405 | 10.287 | 6 | Sch 10S 0.049 · Sch 40S 0.068 · Sch 80S 0.095 |
stainless vs steel — 1/8 (ASME B36.10M)
Measuring this size
- Measure across the pipe, not the fitting: that is the OD, and it is the number a clamp, a hole saw or an insulation sleeve has to match.
- Measured
10.287± a fraction of a millimetre points at NPS 1/8. Check which standards a measurement fits — the same OD can belong to more than one. - The bore decides flow; the wall decides pressure rating and how deep a thread cuts. Neither number is in the name NPS 1/8 carries.
Questions about NPS 1/8
What is the outer diameter of NPS 1/8 pipe?
0.405 in / 10.287 mm — but that is only true for ASME B36.19M. The same nominal label in another standard is a different pipe. Calipers measure this number; the name does not.
What is the inside diameter of NPS 1/8 Sch 40S?
0.269 in / 6.833 mm — the outer diameter minus twice the wall (0.405 − 2 × 0.068). This standard publishes nominal wall, so the bore is exact within manufacturing tolerance. Other wall series for this size are in the table above.
Is NPS 1/8 the same as DN 6?
DN 6 is the millimetre-family name for this size, so yes for the size — no for the number. DN is not the outer diameter and not the bore; NPS 1/8 measures 0.405 in / 10.287 mm outside. See the NPS ↔ DN table for the whole series.
Sources for these numbers
- Enerpac NPS chart (PDF)
- The Takeoff pipe schedule chart
- Octal Steel - ANSI B36.10 & B36.19 dimension chart (PDF)
- checked 2026-09-25
Each wall value in this page's tables was confirmed by two independent publications; the list above is those pairs combined, so a source appears once even when it supports several rows. The outer diameter is published per size, not per wall. Data version 48d86b977106.
No edition year is claimed. These values match ASME B36.19M as published by the sources above, but the specific printing was not verified, so the standard is named without a year.
Next
- Full ASME B36.19M chart (17 sizes)
- OD / ID / wall calculator — measure two, get the third
- About ASME B36.19M