Pipe and Tube Measurement: Understanding the Differences & Proper Terminology

Did you know that there are differences between pipe and tube? The main differences are in the terminology used and is commonly misunderstood and becomes confusing when trying to choose the proper material for your project. These differences will be illustrated below.

But before we take a look at the differences, let’s look at the similarities. Both pipe and tube have two important measurements: The Outside Diameter (O.D.) and the Wall Thickness. In the pipe and tube bending industry 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. Now we’ll look at these differences in more detail.

UNDERSTANDING THE BASICS OF MEASURING TUBE

 Tube O.D. and Wall Thickness

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 example, when you require 1-1/2 in. tube for a project, that is its actual O.D. measurement and you will call out for “1-1/2 inch Tube” when requesting material.

Tube Wall Thickness = Gage
Tubing comes in a variety of Gages, which refers to the wall thickness of the tube. Popular gages of tube used are 10, 11, 12, 13, 14, 16, 18, and 20. The lower the gage number the thicker the tube will be. 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.


CHART OF POPULAR TUBE SIZES & GAGES
This chart gives the most commonly requested tube gage along with the measurements in inches.

 Tube Gage Chart

Putting it All 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 gets a little more complex.

UNDERSTANDING THE BASICS OF MEASURING PIPE

 Pipe O.D.-Schedule-I.D.

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 true and will be explained shortly.

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 gages 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

CHART OF POPULAR PIPE SIZES & SCHEDULES
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.

Putting 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”.

MEASURING TUBE AND PIPE SUMMARY
So when ordering your bent pipe and tube products or designing a project that requires pipe or tube, it is important to know the following:

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

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