Pipe Schedule Chart

What a schedule number actually means, wall thickness for every schedule across the common sizes, and exactly where STD, XS and XXS stop coinciding with the numbered schedules.

Schedules in B36.10M: 14
Numbered schedules: 5, 10, 20, 30, 40, 60, 80, 100, 120, 140, 160
Named weights: STD, XS, XXS
Sizes covered: NPS 1/8 – NPS 36

What a schedule number means

A schedule is a wall-thickness series, not a thickness. Within one schedule the wall grows as the pipe grows, so the pressure the pipe can hold stays roughly constant across the size range. Schedule 40 at NPS 1 is 0.133 in; schedule 40 at NPS 24 is 0.688 in. Same schedule, five times the metal.

The original idea, from Barlow's formula, was that schedule number ≈ 1000 × P/S — working pressure over allowable stress. Modern schedules have drifted from that derivation and are simply tabulated values now, but the intent survives: a higher schedule number is a thicker wall and a higher pressure capability at the same nominal size.

Wall thickness across the schedules

Dimensions are given in inches, with the millimetre equivalent beneath in grey.

ASME B36.10M wall thickness in inches for common sizes across every schedule. A dash means the standard does not publish that combination.
Size	Sch 5	Sch 10	Sch 20	Sch 30	Sch 40	STD	Sch 60	Sch 80	XS	Sch 100	Sch 120	Sch 140	Sch 160	XXS
NPS 1/2	0.0651.65 mm	0.0832.11 mm	—	—	0.1092.77 mm	0.1092.77 mm	—	0.1473.73 mm	0.1473.73 mm	—	—	—	0.1884.78 mm	0.2947.47 mm
NPS 1	0.0651.65 mm	0.1092.77 mm	—	—	0.1333.38 mm	0.1333.38 mm	—	0.1794.55 mm	0.1794.55 mm	—	—	—	0.2506.35 mm	0.3589.09 mm
NPS 2	0.0651.65 mm	0.1092.77 mm	—	—	0.1543.91 mm	0.1543.91 mm	—	0.2185.54 mm	0.2185.54 mm	—	—	—	0.3448.74 mm	0.43611.07 mm
NPS 4	0.0832.11 mm	0.1203.05 mm	—	—	0.2376.02 mm	0.2376.02 mm	—	0.3378.56 mm	0.3378.56 mm	—	0.43811.13 mm	—	0.53113.49 mm	0.67417.12 mm
NPS 6	0.1092.77 mm	0.1343.40 mm	—	—	0.2807.11 mm	0.2807.11 mm	—	0.43210.97 mm	0.43210.97 mm	—	0.56214.27 mm	—	0.71918.26 mm	0.86421.95 mm
NPS 8	0.1092.77 mm	0.1483.76 mm	0.2506.35 mm	0.2777.04 mm	0.3228.18 mm	0.3228.18 mm	0.40610.31 mm	0.50012.70 mm	0.50012.70 mm	0.59415.09 mm	0.71918.26 mm	0.81220.62 mm	0.90623.01 mm	0.87522.22 mm
NPS 10	0.1343.40 mm	0.1654.19 mm	0.2506.35 mm	0.3077.80 mm	0.3659.27 mm	0.3659.27 mm	0.50012.70 mm	0.59415.09 mm	0.50012.70 mm	0.71918.26 mm	0.84421.44 mm	1.00025.40 mm	1.12528.57 mm	1.00025.40 mm
NPS 12	0.1563.96 mm	0.1804.57 mm	0.2506.35 mm	0.3308.38 mm	0.40610.31 mm	0.3759.52 mm	0.56214.27 mm	0.68817.48 mm	0.50012.70 mm	0.84421.44 mm	1.00025.40 mm	1.12528.57 mm	1.31233.32 mm	1.00025.40 mm
NPS 16	0.1654.19 mm	0.1884.78 mm	0.3127.92 mm	0.3759.52 mm	0.50012.70 mm	0.3759.52 mm	0.65616.66 mm	0.84421.44 mm	0.50012.70 mm	1.03126.19 mm	1.21930.96 mm	1.43836.53 mm	1.59440.49 mm	—
NPS 20	0.1884.78 mm	0.2185.54 mm	0.3759.52 mm	0.50012.70 mm	0.59415.09 mm	0.3759.52 mm	0.81220.62 mm	1.03126.19 mm	0.50012.70 mm	1.28132.54 mm	1.50038.10 mm	1.75044.45 mm	1.96950.01 mm	—
NPS 24	0.2185.54 mm	0.2506.35 mm	0.3759.52 mm	0.56214.27 mm	0.68817.48 mm	0.3759.52 mm	0.96924.61 mm	1.21930.96 mm	0.50012.70 mm	1.53138.89 mm	1.81246.02 mm	2.06252.37 mm	2.34459.54 mm	—

This chart shows 11 representative sizes. Open a size page for the complete list of schedules in that NPS.

STD, XS and XXS

Standard weight, extra strong and double extra strong predate the numbered schedules and still appear on drawings and in warehouses. They coincide with numbered schedules only over part of the range:

STD equals schedule 40 from NPS 1/8 through NPS 10. At NPS 12 they diverge — STD is 0.375 in, schedule 40 is 0.406 in — and above NPS 12, STD is 0.375 in in every size.
XS equals schedule 80 from NPS 1/8 through NPS 8. From NPS 10 up, XS is 0.500 in in every size while schedule 80 keeps climbing.
XXS has no numbered equivalent at all. It is its own series, published only through NPS 12, and it is not double the XS wall despite the name.

The S schedules

Schedules written with an S suffix — 5S, 10S, 40S, 80S — belong to ASME B36.19M, the stainless steel pipe standard, not to B36.10M. The S does not mean a thinner wall: in most sizes an S-schedule carries exactly the same wall as the numbered schedule it shares a number with. What differs is the size range B36.19M publishes, and two specific wall thicknesses — 40S at NPS 12, and 80S at NPS 10 and 12. Full comparison →

Every schedule

Schedule 525 sizes Schedule 1030 sizes Schedule 2015 sizes Schedule 3014 sizes Schedule 4030 sizes Standard (STD)34 sizes Schedule 609 sizes Schedule 8028 sizes Extra Strong (XS)34 sizes Schedule 1009 sizes Schedule 12012 sizes Schedule 1409 sizes Schedule 16020 sizes Double Extra Strong (XXS)17 sizes

Common questions

Is schedule 40 the same as standard weight?

Only up to NPS 10. At NPS 12 standard weight is 0.375 in and schedule 40 is 0.406 in, and above NPS 12 standard weight stays at 0.375 in while schedule 40 continues to increase.

Is XXS twice the wall thickness of XS?

No, despite the name. XXS is its own tabulated series. At NPS 4, XS is 0.337 in and XXS is 0.674 in — exactly double there — but at NPS 8, XS is 0.500 in and XXS is 0.875 in, which is not.

What is the difference between schedule 40 and 40S?

Schedule 40 is carbon steel pipe from ASME B36.10M; 40S is stainless pipe from ASME B36.19M. In the smaller sizes the wall thicknesses are identical — they part company only at NPS 12, where 40S is 0.375 in and Schedule 40 is 0.406 in — but the S designation always signals stainless, and B36.19M stops publishing 40S above NPS 12.

Does a higher schedule number mean a smaller bore?

Yes. Outside diameter is fixed for a given NPS, so a thicker wall can only grow inward. Schedule 160 NPS 4 pipe has a bore of 3.438 in against schedule 40's 4.026 in — a 27% loss of flow area.