A pipe’s wall thickness is directly related to its pressure rating, strength, weight and flow capacity, which is determined by the pipe schedule. The correct selection of pipe with the same nominal size and outside diameter (OD) can vary in wall thickness according to the schedule to ensure safe and reliable pipe operation. This Pipe Schedule Chart is for the most popular schedules SCH 5, SCH 10, SCH 20, SCH 40, SCH 80, SCH 160 and XXS, and contains standard wall thickness for various pipe sizes. It aids engineers, buyers and fabricators in scheduling, specification checking and choosing the appropriate pipe for industrial applications. Kalpataru Piping offers a variety of carbon steel, stainless steel, alloy steel and special alloy pipes in various schedules to satisfy the requirement of various industries in the world.

Reading the Schedule Chart: What Changes and What Stays Fixed

Reading a schedule chart across this many columns is easier once you know what stays fixed and what moves. Outer diameter never changes across the row, since it is tied to nominal pipe size rather than schedule, which is why a flange rated for a given NPS accepts any schedule without modification. Wall thickness is the only value that climbs from Schedule 5 toward XXS, and inner diameter shrinks with every step up, since bore is outer diameter minus twice the wall. At small sizes, several schedules collapse onto the same thickness, for example Schedule 40 and STD often match, while at larger diameters the schedules spread apart and STD, 40, XS, and 80 report different figures. Available thickness can also vary by manufacturing method, a distinction covered in our difference between ERW and seamless pipe guide.

Pipe Schedule Chart: Wall Thickness in MM for SCH 5, 10, 20, 40, 80, 160 & XXS

Schedule by Schedule: What Each Wall Thickness Class Is Built For

Schedule 5

Schedule 5, sometimes shown as 5S on stainless tables, is the thinnest standardized wall in general circulation, built almost entirely for low pressure and structural service rather than a rated pressure line. At NPS 4, Schedule 5 runs about 2.11 mm, barely a third of the Schedule 40 thickness, which is why it saves considerable weight and cost on runs that only need to contain a fluid at modest pressure or provide a conduit. Because the wall is so thin, Schedule 5 pipe is rarely threaded, since cutting threads into a thin wall removes too great a share of the remaining material and leaves almost nothing to resist bursting. It shows up most often in low pressure water lines, sprinkler distribution, and stainless steel pipes and tubes where corrosion resistance rather than wall strength is doing the heavy lifting.

Schedule 10

Schedule 10 sits one step up from Schedule 5 and has become the default light duty schedule for stainless steel piping, since ASME B36.19M lists it as 10S with dimensions distinct from the carbon steel Schedule 10 table at larger sizes, a difference worth confirming against the stainless steel pipe dimensions chart before ordering. At NPS 6, Schedule 10 measures roughly 3.40 mm against 7.11 mm for Schedule 40, translating directly into lower material cost and easier handling on long stainless runs. Schedule 10 is common in sanitary process piping, low pressure chemical transfer lines, and HVAC systems where the fluid is not aggressive and pressure stays low. It is rarely specified for carbon steel piping beyond mild service, since the thinner wall leaves little corrosion allowance over the design life.

Schedule 20

Schedule 20 occupies a narrower niche than its neighbors and only appears as a distinct entry at larger nominal sizes, typically NPS 8 and above, where it fills the gap between Schedule 10 and Schedule 30 for moderate pressure service on bigger diameters. At NPS 10, Schedule 20 measures about 6.35 mm, noticeably heavier than Schedule 10 at 4.19 mm but still short of the 9.27 mm figure for Schedule 40. Because it barely exists at small sizes, most buyers only encounter Schedule 20 when specifying larger diameter carbon steel pipe for water transmission, low pressure gas gathering, or structural casing, the kind of sizing decision covered in our carbon steel pipe guide. Schedule 40 would represent more wall thickness and cost than the pressure rating requires, making Schedule 20 a genuine cost saver on large bore projects.

Schedule 40

Schedule 40, together with its near identical STD designation at small and mid range sizes, is the wall thickness most piping professionals picture when nobody specifies otherwise, earning that default status through a broad pressure and temperature envelope. At NPS 6, Schedule 40 measures 7.11 mm, comfortably handling typical plant air, water, and low to moderate pressure service without pushing into the heavier, costlier schedules. Because Schedule 40 and STD converge at nearly every size up through roughly NPS 10, the two labels get used almost interchangeably on purchase orders, though above that range the tables diverge and the distinction matters. Its wide availability, combined with a solid, predictable pressure margin, is why every other schedule tends to get measured against it, a role explained in full in our guide to Schedule 40 steel pipe.

Schedule 80

Schedule 80, paired with the older XS or Extra Strong designation, roughly doubles the wall thickness of Schedule 40 at most sizes and is the natural step up whenever a line runs at higher pressure or needs extra allowance for future corrosion or erosion. At NPS 6, Schedule 80 measures 10.97 mm against 7.11 mm for Schedule 40, a jump that raises both the pressure rating and the weight per meter, a figure best confirmed with a proper steel weight formula rather than estimated by eye. Like Schedule 40 and STD, Schedule 80 and XS match closely at small sizes but separate at larger diameters. Schedule 80 is the common choice for steam lines and threaded connections, particularly on seamless pipe, since the extra wall gives threads enough material to hold pressure safely after machining.

Schedule 160

Schedule 160 sits near the top of the standardized range and is reserved for genuinely demanding pressure and temperature combinations rather than routine piping, since the wall thickness increase over Schedule 80 is substantial at every size where it applies. At NPS 6, Schedule 160 runs 18.26 mm, well over double the Schedule 80 figure, and the resulting bore reduction is significant enough that flow calculations must account for the narrower inside diameter, while the added weight is worth checking against a pipe weight calculator before the order is placed. Schedule 160 typically shows up in high pressure steam service, severe chemical process lines, and select oil and gas applications where the design pressure genuinely demands that much wall, since specifying it without justification adds unnecessary weight, cost, and welding difficulty.

XXS (Double Extra Strong)

XXS, or Double Extra Strong, is the heaviest standardized wall class and predates the modern schedule numbering system, having originated alongside STD and XS before the schedule 5 through 160 series was introduced. Because it developed separately, XXS does not have a schedule number and does not scale predictably against Schedule 160 the way Schedule 80 scales against Schedule 40, so it must be looked up directly rather than estimated. At NPS 6, XXS measures roughly 21.95 mm, thick enough that the bore shrinks dramatically compared to lighter schedules, and at larger diameters XXS is not offered at all since the tables stop listing it beyond a certain size. It remains relevant for extreme pressure, high temperature, or heavily eroding service, most often on heavy wall carbon steel pipes and tubes rather than other alloys.

Final Thoughts

Every schedule from 5 through XXS answers one question: how much wall does this line need, no more and no less, to handle its pressure, temperature, and corrosion allowance safely for its design life. Schedule 5 and 10 belong on light duty and stainless service, Schedule 20 fills a large diameter gap most small bore buyers never see, Schedule 40 remains the dependable default, Schedule 80 steps up for higher pressure and threaded connections, and Schedule 160 and XXS are reserved for genuinely severe conditions where anything lighter would be a real risk. Matching the schedule to the actual pressure calculation, rather than habit or a supplier’s default stock, and rechecking the resulting weight against a stainless steel pipe weight chart on stainless projects, is what keeps a system safe without paying for wall thickness never needed.

Frequently Asked Questions