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.

Pipe

When it comes to the measurement of pipe, it is measured 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.

Tube

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.

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