Understanding DN, PN, and NPS: A Comprehensive Guide to Pipe Measurement and Rating Systems



Pipes are an essential component in various industries, including plumbing, construction, and manufacturing. To ensure seamless integration and optimal performance, pipes are measured and rated using different systems. Among the most commonly used systems are DN (Diameter Nominal), PN (Pressure Nominal), and NPS (Nominal Pipe Size). This comprehensive guide will delve into the intricacies of these measurement and rating systems, shedding light on their significance and helping readers gain a clear understanding.

What is DN?

N, or Diameter Nominal, is a metric-based system used to standardize the internal diameter of pipes. It is widely used in Europe and other metric-based countries. DN provides a standardized size for pipes, making it easier to select fittings, valves, and other components that match the pipe’s diameter. DN is measured in millimeters and corresponds to the approximate internal diameter of the pipe. It is important to note that DN does not represent the actual measurement but rather a reference number that simplifies pipe selection.

Understanding PN

PN, or Pressure Nominal, is a numerical rating system that indicates the maximum pressure a pipe can withstand under standard operating conditions. The PN rating is based on the pipe’s design, material, and construction, and it helps in selecting pipes suitable for specific applications. PN is widely used in Europe and Asia, and it is expressed as a numerical value followed by the unit “bar.” The higher the PN rating, the greater the pressure the pipe can handle safely.

Exploring NPS

NPS, or Nominal Pipe Size, is a North American system used to designate the approximate size of pipes. Unlike DN, which is based on the internal diameter, NPS refers to the outside diameter of the pipe. NPS is a numerical value, followed by the unit “inch.” For instance, NPS 1 indicates a pipe with an approximate outside diameter of 1 inch. NPS is commonly used in the United States and Canada and is associated with the ASME B36.10 and ASME B36.19 standards.

Comparing DN, PN, and NPS

While DN, PN, and NPS serve similar purposes in pipe measurement and rating, they differ in terms of geographical usage, measurement parameters, and units of representation. DN is widely used in metric-based countries, while NPS is primarily used in North America. PN focuses on the pressure capacity of pipes and is used in Europe and Asia. It is important to understand these distinctions to ensure proper selection and compatibility when working with pipes across different regions.

Applications and Considerations

Understanding DN, PN, and NPS is crucial for various industries and applications. Plumbing, construction, oil and gas, and industrial manufacturing are just a few sectors that rely on these measurement and rating systems. When choosing pipes, it is essential to consider factors such as fluid compatibility, pressure requirements, environmental conditions, and regulatory standards. Proper selection and sizing based on DN, PN, or NPS ratings ensure the pipe system’s safety, efficiency, and longevity.


DN, PN, and NPS are fundamental measurement and rating systems used to standardize and select pipes based on their size, pressure capacity, and application. Understanding these systems is crucial for professionals in industries that rely on pipes. By comprehending the differences and applications of DN, PN, and NPS, individuals can make informed decisions, ensuring the compatibility and optimal performance of their pipe systems. With this comprehensive