Pipe Schedule to Wall Thickness

Quick Answer

Pipe schedule is a dimensionless number that defines the wall thickness for a given NPS (Nominal Pipe Size). Common schedules include SCH 5S, 10S, 10, 20, 30, 40, 60, 80, 100, 120, 140, 160, STD, XS (Extra Strong), and XXS (Double Extra Strong). For any given NPS, a higher schedule number means a thicker wall, smaller internal diameter, and higher pressure rating.

The schedule system was introduced by ASME B36.10 (carbon and alloy steel) and ASME B36.19 (stainless steel). Schedules ending in “S” (5S, 10S, 40S, 80S) are defined in B36.19 for stainless steel pipes and are typically thinner than the corresponding carbon steel schedules for larger NPS values.

Schedule to Wall Thickness Table (mm)

NPS	OD (mm)	SCH 5S	SCH 10/10S	SCH 40/STD	SCH 80/XS	SCH 160	SCH XXS
1/2	21.3	1.65	2.11	2.77	3.73	4.78	7.47
3/4	26.7	1.65	2.11	2.87	3.91	5.56	7.82
1	33.4	1.65	2.77	3.38	4.55	6.35	9.09
1-1/2	48.3	1.65	2.77	3.68	5.08	7.14	10.16
2	60.3	1.65	2.77	3.91	5.54	8.74	11.07
3	88.9	1.65	3.05	5.49	7.62	11.13	15.24
4	114.3	2.11	3.05	6.02	8.56	13.49	17.12
6	168.3	2.77	3.40	7.11	10.97	18.26	21.95
8	219.1	2.77	3.76	8.18	12.70	23.01	22.23
10	273.1	3.40	4.19	9.27	15.09	28.58	25.40
12	323.9	3.96	4.57	10.31	17.48	33.32	25.40
14	355.6	3.96	4.78	11.13	19.05	35.71	-
16	406.4	4.19	4.78	12.70	21.44	40.49	-
18	457.2	4.19	4.78	14.27	23.83	45.24	-
20	508.0	4.78	5.54	15.09	26.19	50.01	-
24	610.0	5.54	6.35	17.48	30.96	59.54	-

Values per ASME B36.10 and B36.19. Dashes indicate the schedule is not defined for that NPS.

Important Notes

STD vs SCH 40: For NPS 1/8 through NPS 10, STD (Standard) wall thickness equals SCH 40. For NPS 12 and above, STD equals 3/8 inch (9.53 mm) and is thinner than SCH 40.

XS vs SCH 80: For NPS 1/8 through NPS 8, Extra Strong (XS) equals SCH 80. For NPS 10 and above, XS equals 1/2 inch (12.70 mm) and is thinner than SCH 80.

XXS: Double Extra Strong does not correspond to any specific schedule number. It is a fixed wall thickness for each NPS.

Stainless steel (B36.19): SCH 40S equals SCH 40 for NPS 1/8 to NPS 8. For NPS 10 and above, SCH 40S is thinner than SCH 40 per B36.10.

How to Use This Table

1. Start with the NPS (Nominal Pipe Size) of the pipe from the piping specification
2. Identify the required schedule from the pipe class or line list
3. Read the wall thickness from the table
4. Verify that the wall thickness meets the minimum required thickness from the pressure design calculation

Common Mistake

Assuming that STD always equals SCH 40 and XS always equals SCH 80. This is only true for small bore sizes. For NPS 12 and above, STD and XS have fixed wall thicknesses that are thinner than SCH 40 and SCH 80, respectively. Always verify from the applicable ASME standard.

Read the full pipe sizes guide