Introduction

It’s important to know the standards of defining the pipe size, when we choose pipeline, values and other pipe fitting in industrial and constructional fields. There are two common types of system used all over the world is NSP(Nominal Pipe Size) and DN (Diameter Nominal). They are all use to measure and define the pipeline size, but they are always used in different areas , refers to different units of measurement. In this introduction, we will discuss the main differences between NPS and DN, how to mutual converse, and how to choose between them.

The measure units is the key difference between NPS and DN. Inch is used in NPS, but DN always use millimeter. NPS using inch as units, appears in ANSI/ASME standard in the USA.In Europe standard of ISO 6708, specified DN uses millimeters as the pipe diameter.

May these two systems look alike a lot, but they are different measurement standards based on different areas. It’s necessary to understand the two systems, which can help you work in these areas and ensure compatibility when buying and stalling the pipelines.

Let’s take a closer look at these two different systems.

What Does NPS Stand For?

NPS stands for Nominal Pipe Size. NPS is used in north American pipeline system. Inch is the unit of NPS, to measure the internal diameter of pipeline and pipe fittings.  For example, NPS 6 refer to the pipeline with 6 inches internal diameter.

But we need to know, although NPS refer to the internal diameter of pipeline, it does not always match exactly. For example, NPS 6 refers to the outside diameter(OD) of 6.625 inches, but how long is internal diameter depends on its pipeline wall thickness.

What Does DN Stand For?

DN is diameter nominal, also called Nominal Diameter. It used in Europe and a lot of other regions and areas as metric equivalent unit. Different from NPS, DN uses millimeter as pipeline measurement dimensions. For example, DN 150 stands for a  pipeline with a nominal diameter of 150 mm.

In DN system, we use number to represent the approximate internal diameter, even round to the nearest millimeter. The same as NPS, DN in also used in standard pipeline size, which make it easy to recognize and compatible in other kinds of systems.

How to Convert NPS to DN?

It’s simple to convert between NPS and DN. We often divide DN size by 25, the equal to the NPS size that united in inch. For example, there is a pipeline with DN100, that means its a pipeline with NPS 4.

This formula behave well in larger size pipeline. In the small size, non-integer measurement is not so accurate. If you want precise conversions, you can choose conversion chart.

Why Are NPS and DN Important?

NPS and DN is both important in standardizing pipeline size. When you need to deal with the international projects, it’s even more obvious. NPS is often used in America and Canada, but DN is mostly used in Europe and other countries which use metric system.

Engineers, pipe workers and producers must understand the differences between NPS ans DN, to ensure the compatible of pipe, pipe fitting and valves. If the pipeline size is used improperly, that will cause system malfunction.

NPS vs DN: Applications and Use Cases

• NPS: NPSwhich is popular in North America, is always used in industries, pipeline and construction.It is a standard system for ANSI/ASME projects.
• DN: DNis a standard system for Europe and other countries which use ISO standard. It is also used in some international projects that based on measurement methods based on metrics to achieve consistency and compatibility.

 How to Read NPS and DN Charts

Compared the pipeline size chart of NPS and DN can show their differences. This chart show the nominal size of NPS or DN, and offer the corresponding outside diameter to each pipeline size. Besides, a lot of other charts can also provide the wall thickness and corresponding internal diameter.

For example:

This chart can convert the pipeline size between NPS and DN, and also can ensure compatibility when measure.

Summary

In total, NPS and DN are both systems of measuring pipeline size. But they are based on different measure units ( inch is for NPS, millimeter is for DN ). It’s critical for professionals working in pipeline, construction, and industrial projects, to understand the differences and how to convert, to make sure the compatibility.

NPS and DN systems both have the same aim, that ensure compatibility between pipelines, pipefittings and valves. But they are used in different areas: NPS is mainly used in north America, and DN is mainly used in Europe and other countries. If you want to choose the proper pipe fittings and ensure the pipeline’s compatibility, you need to understand these two systems well.