Pipe Vs Tube

What is the difference between Pipe and Tube?

In short: Tube is measured by outside diameter, pipe is measured by inside diameter.

There is often confusion as to which size die the customer actually needs - Pipe Size or Tubing Size.

Keep in mind that pipe size refers to a nominal - not actual - inside pipe diameter. Schedule refers to the pipe's wall thickness. The actual physical OD is larger than it's nominal OD.

The dimensions provided for tubing on the other hand 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 mater 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.

Why the difference between Pipe and Tube?

Pipes are used to transport something, and tubes to construct something; hence, tubes are defined by the outside diameter and wall thickness (for construction stability), and pipes are measured by inside diameter to allow a calculation for transportation viz., speed, volumes etc. (OD = ID + 2 × WT)


Inside Diameter
Outside Diameter
Wall Thinkness
Pipe Vs Tube Measurement