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 wall thicknesses.
THE BASICS OF MEASURING TUBE
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 Wall Thickness is Gauge
Tubing comes in a variety of gauges, referring to the wall thickness. Popular gauges of tube that are used are 10, 11, 12, 13, 14, 16, 18, and 20. The lower the gauge number the thicker the wall thickness of the tube. For example 10 gauge tube measures out at a .134 in. wall thickness, whereas 20 gauge tube measures out at a .035 in. wall thickness. The gauge measurement also remains consistent among the various tube sizes. For example, the thickness for 10 gauge 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.
Popular Tube Sizes and Gauges
The most commonly requested gauges of tubing are 10, 11, 12, 13, 14, 16, 18 and 20. This is the tube gauge. If you convert this to inches, it looks like this:
10 gauge = .134 inches
11 gauge = .120 inches
12 gauge = .109 inches
13 gauge = .095 inches
14 gauge = .083 inches
16 gauge = .065 inches
18 gauge = .049 inches
20 gauge = .035 inches
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 gauge tube”.
THE BASICS OF MEASURING PIPE
Pipe Outside Diameter
A pipe’s proper “name” is called out by the nominal pipe size, or wall thickness. This is known as “schedule” or Sch. Please see the following chart for outside diameters.
Pipe Wall Thickness = Schedule
Pipe comes in a variety of schedules. Popular schedules are Sch 5, 10, 40, and 80. The measurement of a pipe’s schedule varies among pipe sizes, but the O.D. remains 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.)
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.
**4-1/2 inch pipe is only available in Sch 40 and Sch 80.
To Sum it Up
When ordering custom-formed pipe and tube or designing a project that requires pipe or tube, it is important to know that the tube size name is the true outside diameter measurement of the tube. Tube gauge refers to the wall thickness of the tube and the gauge measurement will be consistent from tube size to tube size. A pipe size name is called out as the wall thickness of the pipe and schedule measurement can vary from pipe size to pipe size. Finally, the pipe O.D. remains the same regardless of the schedule of a particular pipe size.