Wait! There is a difference between Pipe and Tube?

Knowing the answer to this question and how to properly measure each will win you trivia championships!
 
Tube and Pipe are not the same. In simple terms, pipe is a vessel used to most often carry fluids and gas. Tube is used for structural projects like car frames and construction. Once you know what you want the next step is figuring out the size you need.
 
Tube is measured by an exact outside diameter (OD) and wall thickness.
Pipe is measured by a nominal outside diameter (also known as NPS or Nominal Pipe Size) and wall thickness.

NPS is a North American set of standard sizes for pipes used for high or low pressures. The schedule number on a pipe relates to the thickness of the wall on the pipe. The higher the number, the thicker the wall. So Schedule 80 pipe is thicker walled material than Schedule 40 pipe. The Schedule number can be the same on two different sized pipes and yet the actual wall thickness will be different. For example a 1” Schedule 40 pipe has a wall thickness of .133”. Whereas a 2” Schedule 40 pipe has a wall thickness of .145”. So, the bottom line on pipe is that the Schedule number will increase the wall thickness, and the wall thickness changes based on the NPS
 
The dimensions provided for tubing refer to the actual outside diameter. In other words, the actual physical OD of a tube is just the same as it's nominal OD. The size of a tube will keep the same OD no matter what the wall thickness is. For example, the actual outside diameter of 1¼″ pipe is 1.625″ - while 1¼″ tube has a true 1.25″ outside diameter.

Consequently, both the size of tube and pipe is measured by it's OD and the thickness.

You have probably heard pipe and tube used interchangeably—but are they different? The answer to that question is yes! The biggest difference between pipe and tube is their shape. Pipe will always be round however tube can be round, square or rectangular. Below are several other factors that make pipe and tube different.

When it comes to measurement of pipe, it is measure by the inside diameter, often called the nominal diameter.  Nominal Pipe Size (NPS) is a North American set of standard sizes for pipe. The term nominal refers to pipe in non-specific terms and identifies the inside diameter with a non-dimensional number. For example, a 2” nominal steel pipe consists of a family of steel pipe with a 2.375″ diameter.

Pipe also has a wall thickness which is referred to by its schedule. The outside of the pipe is always larger than the inside. The difference between the inside diameter (ID) and the outside diameter (OD) is due to the thickness of the wall. Wall thickness also determines the strength of the pipe. Schedule 40 pipe is the most common, however when extra strength is required schedule 80 is available.

Round tubing is specified by its actual outside diameter and is equal to the corresponding size. The thickness of tube is defined by a gauge number. Tube size will keep the same OD no matter what the wall thickness is. Tubing also has a tighter manufacturing tolerance than pipe.

Determine What You Need for Your Project—Pipe or Tubing

1-1/2″ pipe size flanges have an opening to fit over 1.90″ OD—the actual outside diameter of 1-1/2″ pipe. 1-1/2″ tubing has a true 1.50″ outside diameter. The above shows the difference between a 1-1/2″ pipe flange and a 1-1/2″ tube flange.

Here is a table indicating the actual dimensions for several standard pipe sizes.

Wall Thickness

Nominal Pipe Size

Outside
Diameter

Schedule 5

Schedule 10

Schedule 40

Schedule 80

1/2″
3/4″
1″
1-1/4″
1-1/2″
2″
2-1/2″
3″
3-1/2″
4″
5″
6″

.840″
1.050″
1.315″
1.660″
1.900″
2.375″
2.875″
3.500″
4.000″
4.500″
5.560″
6.630″

.065″
.065″
.065″
.065″
.065″
.065″
.083″
.083″
.083″
.083″
.109″
.109″

.083″
.083″
.109″
.109″
.109″
.109″
.120″
.120″
.120″
.120″
.134″
.134″

.109″
.113″
.133″
.140″
.145″
.154″
.203″
.216″
.226″
.237″
.258″
.280″

.147″
.154″
.179″
.191″
.200″
.218″
.276″
.300″
.318″
.337″
.375″
.432″

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