A pipe schedule is a wall-thickness series. For each nominal pipe size (NPS) the outside diameter is fixed, and a higher schedule means a thicker wall. The chart gives outside diameter and wall thickness for the schedules most often specified for pipe and butt weld fittings, from 1/2" to 12" NPS, per ASME B36.10M (carbon and alloy steel) and ASME B36.19M (stainless steel, 10S).
Wall thickness chart: mm (inches)
| NPS | OD | SCH 10S | SCH 40 | SCH 80 | SCH 160 | XXS |
|---|---|---|---|---|---|---|
| 1/2" | 21.3 (0.840) | 2.11 (.083) | 2.77 (.109) | 3.73 (.147) | 4.78 (.188) | 7.47 (.294) |
| 3/4" | 26.7 (1.050) | 2.11 (.083) | 2.87 (.113) | 3.91 (.154) | 5.56 (.219) | 7.82 (.308) |
| 1" | 33.4 (1.315) | 2.77 (.109) | 3.38 (.133) | 4.55 (.179) | 6.35 (.250) | 9.09 (.358) |
| 1-1/4" | 42.2 (1.660) | 2.77 (.109) | 3.56 (.140) | 4.85 (.191) | 6.35 (.250) | 9.70 (.382) |
| 1-1/2" | 48.3 (1.900) | 2.77 (.109) | 3.68 (.145) | 5.08 (.200) | 7.14 (.281) | 10.15 (.400) |
| 2" | 60.3 (2.375) | 2.77 (.109) | 3.91 (.154) | 5.54 (.218) | 8.74 (.344) | 11.07 (.436) |
| 2-1/2" | 73.0 (2.875) | 3.05 (.120) | 5.16 (.203) | 7.01 (.276) | 9.53 (.375) | 14.02 (.552) |
| 3" | 88.9 (3.500) | 3.05 (.120) | 5.49 (.216) | 7.62 (.300) | 11.13 (.438) | 15.24 (.600) |
| 4" | 114.3 (4.500) | 3.05 (.120) | 6.02 (.237) | 8.56 (.337) | 13.49 (.531) | 17.12 (.674) |
| 6" | 168.3 (6.625) | 3.40 (.134) | 7.11 (.280) | 10.97 (.432) | 18.26 (.719) | 21.95 (.864) |
| 8" | 219.1 (8.625) | 3.76 (.148) | 8.18 (.322) | 12.70 (.500) | 23.01 (.906) | 22.23 (.875) |
| 10" | 273.0 (10.750) | 4.19 (.165) | 9.27 (.365) | 15.09 (.594) | 28.58 (1.125) | 25.40 (1.000) |
| 12" | 323.8 (12.750) | 4.57 (.180) | 10.31 (.406) | 17.48 (.688) | 33.32 (1.312) | 25.40 (1.000) |
Values are nominal wall thicknesses; mill tolerance (typically −12.5% for seamless pipe) applies. XXS is thinner than SCH 160 from 8" upward. Sizes 3-1/2" and 5", other schedules (5S, 20, 30, 60, 100, 120, 140, 40S, 80S) and sizes above 12" are covered in the standards and are not shown here.
Schedule 40 vs STD and Schedule 80 vs XS
Schedule 40 equals Standard (STD) wall up to NPS 10, and Schedule 80 equals Extra Strong (XS) up to NPS 8. Above those sizes they differ: for example 12" STD is 9.53 mm against 10.31 mm for 12" SCH 40, and 12" XS is 12.70 mm against 17.48 mm for 12" SCH 80. Always state both the size and the schedule (or STD / XS / XXS) when ordering pipe or butt weld fittings.
Using the chart with fittings
- Butt weld fittings (ASME B16.9) are ordered by NPS and schedule so their bevel matches the pipe wall.
- Socket weld and threaded fittings (ASME B16.11) are ordered by class, which corresponds to a schedule: see the socket weld vs threaded guide.
This guide is a general reference summarised from the named standards. Always design, specify and inspect to the current edition of the applicable standard and your project specification. Published 2026-10-19.