Pipe or Tube: What is The Difference?

Learn the key terms and measurement guidelines


When you think of pipe and tube, do you think “tomato, tamato”? Do you know that there actually are differences between pipe and tube? These differences are mainly in the terminology which is sometimes misunderstood and can be confusing when trying to choose the proper material for a project. 

Both pipe and tube have two important measurements: The outside diameter (O.D.) and the wall thickness. The most important difference between the two is the terminology used when calling out the proper “name” when referring to the size of material, and in the proper “name” of their wall thicknesses.


Tube Outside Diameter
When tube is measured by the O.D., that measurement is its proper “name” and what the tube will be called out as. For instance, for a 1-1/2 in. tube, you will call out for “1-1/2 inch Tube” when requesting that material. 

Tube O.D. and Wall Thickness

Tube Wall Thickness is Gage
Tubing comes in a variety of gages, which refers to the wall thickness. Popular gages of tube that are used are 10, 11, 12, 13, 14, 16, 18, and 20. The lower the gage number the thicker the wall thickness of the tube. For example 10 gage tube measures out at a .134 in. wall thickness, whereas 20 gage tube measures out at a .035 in. wall thickness. The gage measurement also remains consistent among the various tube sizes. For example the thickness for 10 gage tube will consistently measure .134 inches, whether it is 1-1/2 in. O.D., 2 in. O.D., or 4-1/2 in. O.D. tube. The actual measurements of tubing gages are shown in the chart below.

Popular Tube Sizes and Gages
This chart shows the most commonly requested gages of tubing along with the measurement of the gage in inches.

 Tube Gage Chart


Let's Put it Together
A tube that has an outside diameter measuring 1.5 inches and a wall thickness measuring .065 inches is “named”, or called out as, “1-1/2 inch 16 gage tube”.

Seems pretty simple, right? Well, where tube is straight forward with its explanation, pipe is a little more complex.



Pipe Outside Diameter
When you measure pipe by its O.D. (outside diameter), the true measurement is not what the pipe’s proper “name” will be called out as. Contrary to a tube’s proper “name”, its actual O.D., a pipe’s proper “name” is called out by what we call the Nominal Pipe Size which is NOT the pipe’s actual O.D. measurement. For example what is traditionally called “1-1/2 in. pipe” actually has an O.D. measurement of 1.9 inches, NOT the 1.5 inches that you would think it is. (See chart below for actual outside diameters of Nominal Pipe Sizes)

A common belief is that the nominal pipe size is the obtained by measuring the I.D. (inside diameter) of the pipe; however, this is not accurate and will be explained shortly.

Pipe O.D.-Schedule-I.D.


Pipe Wall Thickness = Schedule
Pipe comes in a variety of schedules (Sch), which refers to the wall thickness of the pipe. Popular schedules of pipe are Sch 5, 10, 40, and 80. Unlike tube gauges that remain consistent among the O.D.s, the measurement of a pipe’s schedule varies among the pipe sizes, but the O.D. will remain the same regardless of the schedule of the pipe. (You can see how the schedule measurement varies among the 1-1/2 inch pipe in the “Varied I.Ds” chart below.)

Nominal Pipe Size = Pipe I.D. Myth Debunked
A pipe’s O.D. will remain the same among the different pipe schedules. It is the schedule that will vary among the nominal pipe sizes. So this means a “1-1/2 in. pipe” will have different I.D.s depending on the schedule of that particular pipe size, therefore, the nominal pipe size will NOT equal the pipe I.D. (See example below) The pipe I.D. can be calculated by taking the pipe outside diameter less 2x the wall thickness.

 Pipe I.D. Formula

 Pipe I.D. Variations


This chart shows the most commonly used pipe sizes and schedules along with their “true” O.D. measurements and wall thicknesses for each type of schedule. You can also see in the chart how the schedule varies among the pipe sizes.

Pipe O.D. Schedule Chart
                                                                            **4-1/2 inch pipe is only available in Sch 40 and Sch 80.

Now Let’s Put it All Together
A pipe that has an O.D. measuring 1.66 inches and a schedule measuring 0.140 inches is “named”, or called out as, “1-1/4 inch schedule 40 pipe”.



When ordering your bent pipe and tube products or designing a project that requires pipe or tube, it is important to know the following: A tube size name IS the true outside diameter measurement of the tube.

  1. Tube gauge refers to the wall thickness of the tube and the gauge measurement will be consistent from tube size to tube size.
  2. A pipe size name is NOT the pipe’s “true” outside diameter. (See Understanding the Basics of Measuring Pipe above.)
  3. Pipe schedule refers to the wall thickness of the pipe and the schedule measurement can vary from pipe size to pipe size.
  4. The pipe O.D. remains the same regardless of the schedule of a particular pipe size. (See Understanding the Basics of Measuring Pipe above.)

For more information on pipe and tube sizing, or to request an estimate please email estimating@sharpeproducts.com.