Steel Pipe Dimensions: Understanding Schedule 40 & 80 Sizes

People don’t always know how to talk about the sizes of steel pipes in the right way, or how to tell the seller what size pipe we’re going to buy. If there were any misunderstandings or if we bought the wrong size, that would be a big problem.

So, what are the right ways to talk about the sizes of steel pipes?

To help you understand better, we’ll explain from the following points of view:

3 characters to describe the size of a pipe

Pipe sizes for carbon steel and stainless steel (ASME B36.10M & B36.19M)

Pipe Size Schedule (Schedule 40 & 80 steel pipe means)

Nominal Pipe Size (NPS) and Nominal Diameter (Nominal Diameter) (DN)

Steel Pipe Dimension Chart (Size chart)

Pipe Weight Class Schedule (WGT)

And finally, we’ll tell you the right way to talk about steel pipe dimensions and sizes.

Steel Pipe Dimension 3 characters

Outer diameter (OD), wall thickness (WT), and pipe length are all parts of a full description of the size of a steel pipe (Normally 20 ft 6 meters, or 40 ft 12 meters).

With these symbols, we could figure out how much the pipe weighed, how much pressure it could handle, and how much it cost per foot or per meter.

Because of this, we must always know the right pipe size.

Steel Pipe Dimensions Chart (Size Chart)

Below is the Pipe Schedule Chart in mm. Click here to see the Pipe Schedule Chart in inches.

Dimension standards for steel pipe

There are different ways to describe the size, outside diameter (OD), and wall thickness (WT) of a steel pipe. ASME B 36.10 and ASME B 36.19 are the main ones.

Relevant standard specification ASME B 36.10M and B 36.19M

Both ASME B36.10 and B36.19 are the standard specifications for the sizes of steel pipes and the things that go with them.

ASME B36.10M

The standard is about standardizing the sizes and shapes of steel pipes. There are seamless and welded types of these pipes, and they can be used in high or low temperatures and pressures.

The pipe is different from the tube (Pipe vs. Tube). In this case, the pipe is used for oil and gas, water, and slurry pipelines. Use ASME B 36.10M as your guide.

In this standard, the outer diameter of a pipe smaller than 12.75 inches (NPS 12, DN 300) must be larger than the nominal pipe size (NPS) or DN (Nominal Diameter).

On the other hand, for all sizes of steel tubes, the outside diameter is the same as the pipe number.

Why do pipe sizes smaller than NPS 12 (DN 300) have different OD

First, we have to agree that all pipe sizes should be marked with their nominal sizes (NPS).

Second, these are based on a standard outside diameter for NPS 1/8 (DN 6) to NPS 12 (DN 300). (O.D.) This O.D. was chosen at first to specify pipe size, but since pipes always have a wall thickness and an internal diameter, this is no longer necessary (ID). For a small pipe, the OD and ID (wall thickness) is not the same size, but as the pipe got bigger, the OD and ID became about the same size.

As there is no connection between the old standard thickness (O.D.) and the nominal size, the standard ASME B 36.10 M accepts both of them.

Steel Pipe Schedule

In ASME B36.10M, pipe schedules are labeled as Standard (STD), Ex-Standard (XS), or Double Extra Strong (XSS); or with Schedule No. 5, 10, 20, 30, 40, 80, 120, 160.

ASME B36.19M

ASTM B36.19M is a standard for the sizes of stainless steel pipes. Both seamless and welded pipes are treated the same in this standard.

Most of the time, this size standard is the same as ASTM B36.10M. Wherever the part is different:

Schedule 10S for NPS 14 to NPS 22 (DN 350-550);
Schedule 40S NPS 12
Schedule 80S NPS 10 and 12.

The thickness of the pipes listed above is different from that of B36.10M, so the letter “S” is added here.

Ways of express pipe dimensions

Use Steel Pipe Schedule, like schedule 40 steel pipes or schedule 80 pipes, to figure out the thickness of the pipe wall.
Nominal Pipe Size (NPS) and DN are used for pipe diameters (Nominal Diameter)
Pipe weight class (WGT), pounds per foot (LB/FT), kilograms per meter (Kg per meter)

What is Steel Pipe Dimensions Schedule?

ASME B 36.10 and many other standards use a method called “steel pipe schedule” to show how long a pipe is. This method is marked with “Sch.” Sch is the abbreviation for “schedule,” which is usually a prefix of a serial number in the American steel pipe standard. Sch 80, 80, for example, is a pipe number from the chart or table ASME B 36.10.

“Since the main use of steel pipes is to move fluids under pressure, the inside diameter is the most important size. This size is used as the nominal bore (NB). So, if a steel pipe is going to carry fluids under pressure, it is very important that the pipe is strong enough and has a thick enough wall. So the pipe schedule, which is abbreviated as SCH, tells us how thick the walls are. ASME is the standard and definition for the pipe schedule in this case.

The pipe schedule formula:

Sch.=P/[ó]t1000 where P is the designed pressure in MPa and [ó]t is the allowable stress of the material at the designed temperature in MPa.

What does SCH mean for the steel pipe dimensions?

We usually use the pipe schedule to describe the parameters of a steel pipe. This is a way to show the thickness of the pipe wall with a number. Sch. is not a wall thickness, but a series of wall thicknesses. Different pipe schedules mean that steel pipes with the same diameter but different wall thicknesses. Most of the time, SCH 5, 5S, 10, 10S, 20, 20S, 30, 40, 40S, 60, 80, 80S, 100, 120, 140, 160 are used to show a schedule. The table number shows how thick the pipe wall is. The higher the pressure resistance, the thicker the pipe wall.

Schedule 40, 80 steel pipe dimension means

If you are new to the pipe business, why do you always see schedule 40 or 80 steel pipe? What kind of material are these pipes made out of?

As you’ve seen in the articles above, Schedule 40 or 80 refers to the thickness of the pipe wall. But why do buyers always look for it?

The reason is as follows:

Schedule 40 and 80 steel pipes are the most common sizes needed in different industries. Because of how much pressure they can handle, a lot of them are always needed.

Material standards for pipes this thick don’t have any limits. You could ask for sch 40 stainless steel pipe, like ASTM A312 Grade 316L, or sch 40 carbon steel pipe, like API 5L, ASTM A53, ASTM A106B, A 179, A252, A333, etc.

What is the Nominal Pipe Size (NPS)?

Nominal Pipe Size (NPS) is a set of standard sizes for pipes used in North America at high or low temperatures and pressures. A nominal pipe size (NPS) based on inches and a schedule number are used to describe the size of a pipe (Sched. or Sch.).

What is DN (Nominal Diameter)

Nominal diameter also means outside diameter. Because the pipe wall is so thin, the outside diameter and the inside diameter of a steel pipe are almost the same, so the diameter of the pipe is the average of the two. DN, which stands for “nominal diameter,” is the general diameter of different pipes and pipe parts. Pipes and pipe fittings with the same nominal diameter can be joined together. This is called interchangeability. Even though the value is close to or the same as the pipe’s inside diameter, it is not the same as the pipe’s diameter. The nominal size is shown by a digital symbol and the letter “DN.” After the symbol, write the unit in millimeters. For instance, DN50 refers to a pipe whose nominal diameter is 50 mm.

DN (mm) and NPS (inch) conversion

Nominal diameter DN (mm) and NPS (inch) conversion

Conversion DN ( mm ) that requires separate memory

DN (mm) | 6 | 8 | 10 | 15 | 20 | 25 | 32 | 40 | 50 | 65 | 80 |

NPS(inch) | 1/8 | 1/4 | 3/8 | 1/2 | 3/4 | 1 | 1-1/4 | 1-1/2 | 2 | 2-1/2 | 3 |

Diameter equal to or greater than DN100 and NPS conversion

DN=25*NPS;
NPS=DN/25

Exact conversion 1 inch = 25.4 mm

Pipe Weight Class Schedule

WGT class, which stands for “weight class,” was used to show how thick the pipe wall was. It is still used. It only comes in three grades: STD (standard), XS (extra strong), and XXS (extra strong) ( double extra strong ).

For older pipes, each caliber has only one standard, which is called a “standard tube” (STD). The thickening pipe (XS) was made so that fluids under high pressure could be moved. The higher pressure fluid seemed to be fine with XXS (double extra strong) pipe. People started to want to use thin-walled pipes because they were cheaper. When new technology for processing materials came along, the above pipe number slowly started to show up. ASME B36.10 and ASME B36.19 specifications explain the relationship between pipe schedule and weight class.

How to describe steel pipe dimensions and size correctly?

For example,

Written as “pipe outside diameter wall thickness,” such as 88.9mm x 5.49mm (3 1/2″ x 0.216″). 114.3mm x 6.02mm (4 1/2″ x 0.237″), length 6m (20ft) or 12m (40ft), Single Random Length (SRL 18-25ft), or Double Random Length (DRL 38-40ft)
Written as “NPS x Schedule”: NPS 3 inch x Sch 40, NPS 4 inch x Sch 40. The same size as what was said above.
Written as “NPS x WGT Class,” “NPS 3” x “SCH STD,” or “NPS 4” x “SCH STD.” Same size as above.
There is another way to describe pipe size. In North America and South America, people usually use “Pipe Outer Diameter x lb/ft.” As OD 3 1/2″, 16.8 lb/ft. A pound per foot is what lb/ft stands for.

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Frequently asked questions

The size of a steel pipe is primarily described by its outer diameter (OD), wall thickness (WT), and length. The outer diameter represents the overall width of the pipe, while the wall thickness indicates how thick the pipe walls are. The length of the pipe is usually specified as 20 feet (6 meters) or 40 feet (12 meters). Knowing these dimensions is crucial for determining the pipe's weight, pressure capacity, and cost.

Nominal Pipe Size (NPS) and Nominal Diameter (DN) both describe the size of a pipe but use different systems. NPS, commonly used in North America, is based on inches and refers to standard pipe sizes, such as NPS 4 for a pipe with a nominal diameter of 4 inches. On the other hand, Nominal Diameter (DN) is an international standard expressed in millimeters, such as DN 100 for a pipe with a nominal diameter of 100 mm. While DN values are close to the pipe's outside diameter, NPS values are nominal and may not match the actual dimensions.

Pipe schedules define the wall thickness of steel pipes, impacting their pressure ratings and applications. For instance, Schedule 40 is a common choice for standard applications due to its moderate wall thickness, whereas Schedule 80 pipes are used for higher pressure situations due to their thicker walls. The schedule number reflects the pipe's strength and suitability for various pressure levels, with higher numbers indicating thicker walls and greater pressure capacities.