Understanding Nominal Pipe Size (NPS), Nominal Bore (NB), and Nominal Diameter (DN)

When working in the plumbing and drain cleaning industry, understanding the different measurements and standards is essential for selecting the right tools and materials. Among the most important terms you'll encounter are Nominal Pipe Size (NPS), Nominal Bore (NB), and Nominal Diameter (DN). These measurements are crucial in ensuring compatibility and efficiency in your work. In this blog post, we’ll break down these terms and explain how they relate to each other.

What is Nominal Pipe Size (NPS)?

Nominal Pipe Size (NPS) is a North American standard for indicating pipe sizes. It is primarily used in the United States and Canada and is based on the diameter of the pipe. However, NPS doesn’t refer to the actual outside or inside diameter of the pipe. Instead, it’s a designation that helps standardize the size of pipes across different manufacturers.

• Example: A pipe with a NPS of 2 inches doesn’t necessarily have an outside diameter of 2 inches. For instance, a 2-inch NPS pipe actually has an outside diameter of 2.375 inches.

NPS is used for both seamless and welded pipes and applies to pipes used in a variety of applications, including plumbing, HVAC, and industrial processes.

What is Nominal Bore (NB)?

Nominal Bore (NB) is another term often used interchangeably with NPS, particularly in the UK and other regions following British standards. NB essentially refers to the same concept as NPS, which is the approximate internal diameter of the pipe, not the exact measurement.

• Example: A 2-inch NB pipe would have the same meaning as a 2-inch NPS pipe in terms of its usage and sizing.

NB is crucial when specifying pipes in projects that require compatibility with existing systems, especially in international contexts where different measurement standards might be used.

What is Nominal Diameter (DN)?

Nominal Diameter (DN), as explained in our previous blog post, is the European standard for pipe sizing used with metric measurements.

• Example: A DN50 pipe refers to a pipe with an approximate internal diameter of 50 millimeters, but again, this is not an exact measurement.

DN is used extensively in Europe and other parts of the world where the metric system is the standard. It’s important to note that DN sizes don’t correspond directly with NPS or NB sizes, but they serve a similar purpose in standardizing pipe sizes.

How Do These Terms Relate to Each Other?

While NPS, NB, and DN are used in different regions and standards, they all serve the same fundamental purpose: to standardize pipe sizes for consistency and compatibility across different systems and manufacturers. You can find more information about the pipe size classifications here.

• NPS (Nominal Pipe Size) and NB (Nominal Bore) are essentially equivalent, both referring to the approximate internal diameter of a pipe in imperial measurements.
• DN (Nominal Diameter) is the metric equivalent, used primarily in Europe and countries that follow the metric system.

When working on international projects or selecting tools and materials that may be used across different regions, understanding the relationship between NPS, NB, and DN is critical. This ensures that you’re selecting the correct size pipe or tool, reducing the risk of errors or incompatibilities.

The DN (Diameter Nominal), NPS (Nominal Pipe Size), and NB (Nominal Bore) measurements are related but not directly interchangeable or fixed to each other in all cases. However, they are often used together to describe the size of pipes, particularly in contexts involving both metric and imperial systems.

DN (Diameter Nominal): A metric system designation that represents the approximate internal diameter of a pipe in millimeters.

NPS (Nominal Pipe Size): An imperial system designation used in North America, representing the nominal diameter of the pipe, not its exact inside or outside diameter.

NB (Nominal Bore): Often used interchangeably with NPS, referring to the approximate internal diameter of the pipe.

Here’s a chart that shows the relationship between DN (Diameter Nominal), NPS (Nominal Pipe Size), and their approximate corresponding dimensions.

Conclusion

In summary, Nominal Pipe Size (NPS), Nominal Bore (NB), and Nominal Diameter (DN) are all essential terms in the plumbing and drain cleaning industry. They help standardize pipe sizes, making it easier to select the right tools and materials for the job. By understanding these terms and how they relate to each other, you can make more informed decisions and ensure your projects run smoothly, regardless of where you are in the world.

Remember, whether you're working with NPS, NB, or DN, the key is to match the size designation with the appropriate tools and pipes to ensure a perfect fit and efficient operation.