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What is the difference between pipe and tube ID?

Feb. 04, 2024

One of the first questions we ask customers as we learn more about their application is, “Are you dealing with pipe or tube?” Even those who have years of experience in the industry use the terms interchangeably, however, there is variation between the two when it comes to size, nomenclature and even shape. It is important to know the difference between pipe and tube to learn more about your application. Having this knowledge should allow you to purchase or rent the right tools and equipment.

What Industries Use Pipe & Tube

Common pipe and tube industries:

  • Aerospace – Tube
  • Brewery/Distillery - Both
  • Food/Dairy/Beverage - Tube
  • Chemical/Petrochemical - Both
  • Pharmaceutical/Biopharmaceutical - Tube
  • Power Generation – Both
  • Pulp/Paper - Both
  • Oil/Gas – Pipe
  • Semiconductor - Tube
  • Shipbuilding - Both
  • Wastewater Treatment – Pipe

Measuring Pipe vs Tube

Though there are many differences between tube and pipe, the most significant difference is found in the size and way they are measured. Tube is measured by outside diameter (OD) and wall thickness. Because tube is used in structural applications, OD is the most important dimension to consider. The OD is measured in actual sizes. Simply if you are using 2” tube – your piece of tube measures 2” across from the outside of the tube to the other side. As the inside diameter (ID) changes the outside diameter stays the same.

Now, here is when it gets tricky. Pipe is measured in Nominal Pipe Sizes (NPS), inside diameter and schedule (wall thickness). The actual OD for pipe can be calculated from the equation:

OD = ID + 2 * Wall Thickness

Let us compare 2” Tube and 2” Pipe. As you can see below, a piece of 2” tube has the same 2” OD no matter the wall thickness. When it comes to pipe, the actual OD is 2.375” even if the wall thickness is the same as the 2” Tube.

When it comes to pipe, referencing a pipe chart like the one below can help you quickly find the measurements you need.

Pipe Chart Pipe Size Schedule Wall ID 1/8" 10S 0.049 0.307 40ST, 40S 0.068 0.269 80XS, 80S 0.095 0.215 1/4" 10S 0.065 0.41 40ST, 40S 0.088 0.364 80XS, 80S 0.119 0.302 3/8" 10S 0.065 0.545 40ST, 40S 0.091 0.493 80XS, 80S 0.126 0.423 1/2" 5S 0.065 0.71 10S 0.083 0.674 40ST, 40S 0.109 0.622 80XS, 80S 0.147 0.546 160 0.188 0.464 XX 0.294 0.252 1" 5S 0.065 1.185 10S 0.109 1.097 40ST, 40S 0.133 1.049 80XS, 80S 0.179 0.957 160 0.25 0.815 XX 0.358 0.599 1 1/4" 5S 0.065 1.53 10S 0.109 1.442 40ST, 40S 0.14 1.38 80XS, 80S 0.191 1.278 160 0.25 1.16 XX 0.382 0.896 1 1/2" 5S 0.065 1.77 10S 0.109 1.682 40ST, 40S 0.145 1.61 80XS, 80S 0.2 1.5 160 0.281 1.338 XX 0.4 1.1 2" 5S 0.065 2.245 10S 0.109 2.157 40ST, 40S 0.154 2.067 80XS, 80S 0.218 1.939 160 0.344 1.687 XX 0.436 1.503 2 1/2" 5S 0.083 2.709 10S 0.12 2.635 40ST, 40S 0.203 2.469 80XS, 80S 0.276 2.323 160 0.375 2.125 XX 0.552 1.771 3" 5S 0.083 3.334 10S 0.12 3.26 40ST, 40S 0.216 3.068 80XS, 80S 0.3 2.9 160 0.438 2.624 XX 0.6 2.3 3 1/2" 5S 0.083 3.834 10,10S 0.12 3.76 40ST, 40S 0.226 3.548 80XS, 80S 0.318 3.364 XX 0.636 2.728 4" 5S 0.083 4.334 10, 10S 0.12 4.26 40ST, 40S 0.237 4.026 80XS, 80S 0.337 3.826 120 0.438 3.624 160 0.531 3.438 XX 0.674 3.152 4 1/2" 40ST, 40S 0.247 4.506 80XS, 80S 0.355 4.29 XX 0.71 3.58

Other Differences Between Tube & Pipe


Pipe is always round while tube can vary in shape. While the tube we work with in the orbital welding industry is always round, there is also square and rectangular tube.


Pipe has a looser tolerance than tube, especially in larger OD sizes. This includes: Diameter Tolerance, Wall Thickness/Weight Tolerance, Straightness Tolerance, Roundness (Ovality) Tolerance.

Orbital Tube Welding vs Orbital Pipe Welding

Most tube sizes and small pipe can be welded through the fusion process. This type of orbital welding is done with enclosed weld heads. The process fuses existing material and creates a clean, sanitary weld optimal for critical industries that process items that cannot risk contamination, such as food and pharmaceuticals. Fit up is critical for this type of weld and requires the proper cutting and tube facing tools.

Large orbital pipe welding is performed with open face style weld heads and added filler wire. Due to heavy pipe walls, a bevel is necessary - otherwise, there would not be full penetration during the weld. Filler wire replaces the metal that was removed during the bevel. This usually calls for multiple orbits or “passes” around the pipe seam. Lose tolerances on pipe can be combated with tracking rollers and AGC – stay tuned for our next blog with more details on this process.

It is important to communicate the details of your tube and pipe application with your purchasers and key decision-makers so that they are informed when purchasing equipment. With the right information, Morgan Industrial Technology can find the right solution.


The Difference Between a Pipe and a Tube

In the manufacturing industry one often hear terms such as steel pipes or steel tubing. Often times, it is often not clear what the difference is between a pipe and a tube.

Many people think that the word has the exact same meaning and use the word "pipe" and "tube" interchangeably. That's however wrong.

There are a couple of key differences between tubes and pipes:

  • A pipe is a vessel - a tube is structural
  • A pipe is measured in terms of its ID (inside diameter)
  • A tube is measured in terms of its OD (outside diameter).

A hollow cylinder has 3 important dimensions. These dimensions are:

  • The Outside Diameter (OD)
  • The Inside Diameter (ID), and
  • The wall thickness (wt)

These three dimensions are related by a very simple equation:

OD = ID + 2*wt

One can completely specify a piece of pipe or tube by supplying any two of these numbers.

Tubing is typically used in structures so the OD (or Outside Diameter) is the important number. The strength of a steel tube depends on its wall thickness. So tubing is specified by the outside diameter as well as its wall thickness. Steel tubes are also not only supplied in round sections but can be formed into square and rectangular tubes.  

Pipes are normally used to transport gases or fluids so it is important to know the capacity of the pipe. Here the internal cross-sectional area defined by the ID (or Inside Diameter) is important. It is common to identify pipes in inches by using NPS or "Nominal Pipe Size". The metric equivalent is called DN or "diameter nominal". The metric designations conform to International Standards Organization (ISO) usage and apply to all plumbing, natural gas, heating oil, and miscellaneous piping used in buildings. A plumber always knows that the id on the pipe label is only a *nominal* id.

As an example, a (nominal) 1/8" wrought iron pipe will typically have a *measured* id of 0.269" (schedule 40) or 0.215" (schedule 80).  The key in the difference is the application where both tube and pipe are used for. For instance: a (nominal) 1/8" schedule 40 pipe will have a wall thickness of 0.068 (id=0.269) while a 1/8" schedule 80 pipe will have a wall thickness of 0.095 (id=0.215). And these schedule numbers do not reflect a constant wall thickness. For instance, a (nominal) 1/4 schedule 40 pipe has a wt=0.088 while the same pipe in schedule 80 has wt=0.119

Generally speaking, a tube will have a consistent OD and its ID will change. Steel tubes used in structural applications would most likely be seam welded while pipes are normally a seamless steel product. Some steel tubes are also used in the transport of fluids, even though they are seam welded. These include steel tubes for water pipes and welded tubes are commonly used in the agricultural industry for manufacturing spindles. Such tubes will undergo a process called pressure testing were the tube is sealed at both ends and water is pumped through the tube up to a certain level of pressure. This will quickly indicate if there is a lead or a bad spot in the weld of the circular hollow section tested.

What is the difference between pipe and tube ID?

The Difference Between a Pipe and Tube


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