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In the world of pipes and tubing, it’s crucial to have a clear understanding of the specifications and standards that dictate their dimensions and performance. One such important factor is the thickness of pipes, often referred to as “schedule.” In this comprehensive guide, we will delve into the concept of schedule 40 pipe thickness in mm (in mm) to provide you with a clear understanding of what it is, how it’s measured, and its significance in various industries.

What is Schedule 40 Pipe Thickness (in mm)?

Schedule 40 pipe thickness (in mm) refers to the standardized wall thickness of a pipe, particularly in the context of steel pipes. The schedule number, in this case, “40,” represents the nominal thickness of the pipe wall. It is important to note that the schedule number does not correspond directly to the actual thickness in millimeters. Instead, it is a designation that helps ensure uniformity and compatibility in pipe systems.

Key Points about Schedule 40 Pipe Thickness (in mm):

  1. Nominal Thickness: Schedule 40 specifies a nominal thickness rather than an exact measurement. This nominal thickness ensures that pipes of the same schedule are compatible and can be joined together seamlessly.
  2. Standardization: The use of schedule numbers is a standardized system adopted across the industry, making it easier for manufacturers, engineers, and users to communicate about pipe specifications.
  3. Variety of Materials: Schedule numbers are used not only for steel pipes but also for pipes made of other materials like PVC, CPVC, and copper. Each material may have its own set of schedule numbers.

How to Read and Interpret Schedule 40 Pipe Thickness (in mm)

Understanding the schedule 40 designation requires interpreting a specific code that includes both the schedule number and a corresponding wall thickness. In the case of steel pipes, the nominal wall thickness for schedule 40 is usually expressed in inches. To convert it to millimeters, you can use the following formula:

1 inch = 25.4 millimeters

So, if we take the nominal thickness for schedule 40, which is approximately 0.133 inches, and convert it to millimeters:

0.133 inches x 25.4 millimeters/inch = 3.38 mm

Therefore, schedule 40 steel pipes have a nominal wall thickness of approximately 3.38 mm.

Significance of Schedule 40 Pipe Thickness (in mm)

The schedule number, along with its corresponding thickness in millimeters, plays a crucial role in various industries and applications:

1. Plumbing and Water Supply

In residential and commercial plumbing systems, schedule 40 pipes are commonly used for water supply lines. The standardized schedule ensures that pipes from different manufacturers can be interconnected reliably. The 3.38 mm thickness provides adequate strength to withstand the pressure of flowing water.

2. Industrial Pipelines

In industrial settings, the schedule 40 designation simplifies the selection and installation of pipes for various applications, including conveying chemicals, gases, and other fluids. The uniformity in wall thickness ensures consistent performance and reliability.

3. Construction and Structural Applications

Schedule 40 steel pipes are utilized in construction and structural applications for their strength and durability. The 3.38 mm thickness makes them suitable for building support structures, handrails, and scaffolding.

4. HVAC Systems

Heating, ventilation, and air conditioning (HVAC) systems often rely on schedule 40 pipes for ductwork and ventilation. The standardized schedule simplifies system design and maintenance.

5. Oil and Gas Industry

In the oil and gas sector, schedule 40 pipes are used for various purposes, including transporting crude oil and natural gas. The consistent wall thickness ensures the integrity of these critical pipelines.

Other Common Schedule Numbers

While schedule 40 is widely used, there are other schedule numbers that correspond to different wall thicknesses, each suited for specific applications. Here are a few examples:

1. Schedule 10

Schedule 10 pipes have a thinner wall compared to schedule 40, making them suitable for less demanding applications where pressure and strength requirements are lower. The approximate thickness in millimeters is 2.77 mm.

2. Schedule 80

Schedule 80 pipes, on the other hand, have a thicker wall than schedule 40, providing greater strength and durability. The approximate thickness in millimeters is 5.56 mm. These pipes are commonly used in high-pressure applications.

3. Schedule 160

Schedule 160 pipes have an even thicker wall compared to schedule 80, making them suitable for extremely high-pressure applications. The approximate thickness in millimeters is 11.13 mm.


Understanding sch 40 pipe thickness (in mm) is crucial for anyone involved in selecting, installing, or maintaining pipes in various industries. It represents a standardized system that simplifies the process of choosing the right pipes for specific applications. The 3.38 mm nominal thickness of schedule 40 steel pipes strikes a balance between strength and versatility, making them suitable for a wide range of uses, from plumbing to construction and industrial pipelines. Whether you’re a plumber, engineer, or involved in any field where pipes are essential, having a clear grasp of schedule numbers and their corresponding wall thickness is indispensable for ensuring the success and reliability of your projects.

About the Author

Justin Brandon