Pipe Size Chart | NPS, DN, NB, Outside / Inside Diameter, Wall Thickness

Before the invention of pipes, people used to carry water from lakes, ponds and reservoirs to their homes and fields. As this was a time consuming and tedious job, the idea of pipe was born using bamboos. But since the mid 1800’s, steel pipe became popular in the U.S. to carry water. Pipes are used in residential, commercial, industrial and agricultural applications to carry water, fuel, gases and other fluids. As different sizes of pipes are needed for different types of jobs, it is essential to grasp how the pipe sizes work with the help of a Pipe Size Chart.

So, in this article, we will learn about different types of pipes, the nomenclature associated with pipe size and also a pipe size chart for commonly used pipe sizes.

Pipes and Types of Pipes

In a general sense, a pipe is nothing but a hollow and tubular structure that is used to carry liquids, gases and fluids in general. Depending on the application, cost and other factors, pipes are made from a variety of materials. Some of the popular piping materials are:

• Copper
• Aluminum
• Cast Iron
• Plastic
• Lead
• Glass
• Brass
• Steel
• Steel Alloys

1. Steel Pipe

It is one of the popular types of pipes used in high pressure and temperature situations to transport water, oil, gas and steam. In fact, since 1850s, steel pipes are used in the U.S. to carry water. Depending on their cross-sectional configuration, steel pipes are usually classified into Standard, Extra Strong and Double Extra Strong.

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2. Plastic Pipe

Modern day’s piping consists of mostly Plastic Pipes as they are cheaper to manufacture, easy to install and have higher resistance to corrosion. They are used to carry water, gas and oil but rarely used where temperature and pressure plays a major factor.

3. Cast Iron Pipe

Another popular pipe type is the Cast Iron Pipe. It is generally used to carry water, gas and drainage in the underground. Low-pressure steam can also be transported using cast iron pipes.

4. Copper Pipes

If corrosion is a main concern, then Brass or Copper Pipes can be used as an alternative to steel or cast-iron pipes. They have significantly better resistance to corrosion and can last longer when used in a corrosion prone environment. Copper pipes are also used in industrial application involving hydraulic and pneumatic systems.

Pipe Sizing

With the advancement in manufacturing process of pipes, we are able to produce pipes with specific characteristics such as its strength, temperature and pressure ratings, corrosion resistance, thickness and size. As there are multiple ways to categorize pipes, be it its manufacturing process, its final form or other characteristics, categorizing pipes based on size is a simple and basic method.

Different institutes and organizations have put a lot of effort into standardizing pipe sizes. One such organization is the American National Standards Institute (ANSI), which standardized pipe sizes, color code, nameplates and legends.

Typically, a pipe has four characteristics to be categorized based on size. They are:

• Nominal Pipe Size
• Outer Diameter
• Inner Diameter
• Wall Thickness

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From the above image, you can easily understand the different dimensions of a pipe.

What is Nominal Pipe Size, Nominal Bore and Nominal Diameter in Pipe Sizes?

Nominal Pipe Size or NPS is an easy way to identify pipes based on a vague representation of the outer diameter of the pipe. It is used in the Unites States and it is just a “nominal” size of the pipe without any dimensions.

For example, an NPS 6 doesn’t exactly have its outer diameter of 6inches. It is actually 6.625inches. Another important point to note about NPS representation is for NPS 1/8 to NPS12, the diameter is measured from the center of the wall. Hence, the outer diameter will be slightly higher than the NPS value.

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But from NPS14 onwards, the outer diameter and the NPS values are the same. So, NPS14 corresponds to a pipe with 14inch outer diameter.

While NPS is predominantly used in the U.S., the term Nominal Bore or NB is NPS equivalent in Europe (and other parts of the World). Except for the difference in names, both NPS and NB are the same.

Nominal Diameter (sometimes Diameter Nominal) or DN is the metric representation of the pipe size and hence the units are in millimeter. It is used everywhere in the World except North America. DN measures the inner diameter of the pipe and is roughly equal to 25 times the NPS.

Pipe Wall Thickness and Scheduling

The pipe wall thickness is an important dimension associated with pipes. Like NPS, even the wall thickness is denoted using a simple naming system called Schedule (SCH). Higher the wall thickness or schedule, greater is the strength of the pipe.

Originally, pipe wall thickness is categorized into three types:

• Standard (Std)
• Extra Strong (XS)
• Double Extra Strong (XXS)

The usage of pipes in industries and different pressure and temperature environments lead to new pipe wall thickness nomenclature.

• SCH5
• SCH10
• SCH10S
• SCH20
• SCH30
• SCH40
• SCH40S
• SCH60
• SCH80
• SCH80S
• SCH100
• SCH120
• SCH140
• SCH160

In the new schedule naming system, the following can be observed:

• For NPS1/8 to NPS10, Standard (Std) Schedule is similar to SCH40 and SCH40S.
• For NPS1/8 to NPS8, Extra Strong (XS) Schedule is similar to SCH80 and SCH80S.
• Foe NPS1/8 to NPS6, Double Extra Strong (XXS) Schedule is similar to SCH160.
• For NPS8 and larger size pipes, SCH160 is thicker than XXS.

Pipe Size Chart

If you are new to pipes and its terminology, then Pipe Sizes can be confusing. Earlier, the pipe size was based on the inner diameter of the pipe. But this system had problems when using pipe fittings for the outer diameter.

Now-a-days, Pipe Sizes generally consists of Outer (or Outside) Diameter (sometimes NPS) and Wall Thickness. Let us now see some pipe size charts for commonly used pipe sizes.

In the first Pipe Size Chart, we will list out all the common pipe sizes until (and including) NPS12 as this is the limit where NPS and Outer Diameter are different. In the second pipe size chart, we will list out all the common pipe sizes starting from NPS14.

Pipe Size Chart for NPS1/8 to NPS12

For the sake of simple visual representation, we will further split the table into multiple sections as there are too many rows to fill.