Pipe schedule chart

What a schedule number means

Every nominal pipe size (NPS) has one outside diameter. The schedule sets the wall thickness, so a heavier schedule keeps the same OD and shrinks the bore. ASME B36.10M standardizes the dimensions of welded and seamless wrought steel pipe; ASME B36.19M does the same for stainless steel pipe.

A schedule is not a fixed wall. Schedule 40 grows with the pipe: 0.109 in at 1/2 in, 0.154 in at 2 in, 0.280 in at 6 in and 0.406 in at 12 in. Pressure ratings are not on this chart; get them from the piping code and the manufacturer's data for the job.

STD, XS and XXS vs schedule numbers

B36.10M carries two naming systems side by side, as InfraBuild's chart shows: the weight classes Standard (STD), Extra Strong (XS) and Double Extra Strong (XXS), and schedule numbers from 10 to 160. They overlap for small pipe and split for large pipe:

• STD and Schedule 40 are the same wall through NPS 10. At 12 in, STD is 0.375 in and Schedule 40 is 0.406 in.
• XS and Schedule 80 are the same through NPS 8. At 10 in, XS is 0.500 in and Schedule 80 is 0.594 in.
• XXS is not always heavier than Schedule 160. At 2 in, XXS is 0.436 in against 0.344 in for Schedule 160; at 8 in, XXS is 0.875 in against 0.906 in.

Mill literature does not always follow the split. Wheatland's brochure lists its 12 to 18 in ERW pipe as Schedule 40 at a 0.375 in wall, which is the STD wall; B36.10M Schedule 40 at 12 in is 0.406 in. On large pipe, check the actual wall thickness rather than trusting the words Schedule 40.

Stainless schedules: 5S, 10S, 40S, 80S

B36.19M adds the S schedules for stainless pipe; ASME notes that the S suffix separates B36.19M pipe from B36.10M pipe. 5S and 10S are thin walls; 2-inch 5S is 0.065 in and 10S is 0.109 in. 40S and 80S match STD and XS through NPS 12, so at 12 in 40S is 0.375 in, the STD wall, not the 0.406 in of Schedule 40. InfraBuild's B36.19 chart lists no 40S or 80S above 12 in. From 14 to 22 in, ASME notes that 10S differs from B36.10M: 14-inch 10S is 0.188 in, against 0.250 in for carbon steel Schedule 10.

Some supplier charts also list a carbon steel Schedule 10 for small pipe at the same walls as 10S: Alro's carbon pipe pages give Schedule 10 as 0.083 in at 1/2 in and 0.109 in at 2 in. InfraBuild's B36.10 chart starts Schedule 10 at NPS 14, so this chart lists those smaller walls under 10S.

Inside diameter and weight

ID = OD - 2 x wall. For 1-inch Schedule 40: 1.315 - 2 x 0.133 = 1.049 in. The chart gives every ID to 0.001 in and in mm. ASTM A53, as Wheatland lists it, lets the wall run up to 12.5% under nominal at any point, so a measured ID can differ from the chart.

Weight (lb/ft) = 10.69 x (OD - wall) x wall, with OD and wall in inches, for plain-end carbon steel. InfraBuild publishes the metric form, 0.02466 x (D - t) x t kg/m with D and t in millimeters; converted to inches and pounds per foot the factor becomes 10.69. For 2-inch Schedule 40: 10.69 x (2.375 - 0.154) x 0.154 = 3.66 lb/ft, the figure in Wheatland's A53 tables. Alro stocks carbon pipe in 21 and 42 ft lengths; a 21 ft length of 2-inch Schedule 40 weighs about 77 lb. InfraBuild gives a factor of 1.015 for the mass of austenitic stainless pipe, so stainless pipe of the same size weighs about 1.5% more.

Metric sizes

ASME also gives each size a metric designation, DN (diameter nominal): NPS 12 is DN 300. InfraBuild's chart pairs the two names on each row: NPS 1/2 is DN 15, NPS 2 is DN 50, NPS 4 is DN 100. The pipe is the same; only the name differs. The chart gives OD and wall in mm next to inches; InfraBuild's B36.10 chart lists 2-inch Schedule 40 as 60.3 mm OD with a 3.91 mm wall.

ASME notes that pipe of NPS 12 and smaller has an outside diameter numerically larger than its size. From NPS 14 up, the NPS equals the OD in inches: 14-inch pipe is 14.000 in (355.6 mm) OD. Below that, the NPS is only a name, which is why 1/2-inch pipe measures 0.840 in. The pipe size chart maps nominal sizes to actual ODs for steel, PVC and copper tube side by side.