651-432-4050 Sales@StPaulSign.com

Confused about Pipe Schedule vs Tube Gauge meanings? Confused as to why 6″ Pipe does not have a 6″ diameter?

Nominal Size

Nominal pipe sizes are given by their inner diameter (ID) while nominal round tube sizes are given by their outer diameter (OD). So a 6″ inch pipe might have an OD of 6.5″. “Nominal” means “in name only”.

A 2×4 is not 2″ by 4″

Like when you buy 2x4s, you know they aren’t actually 2″ by 4″, but 1.5″ by 3.5″. Yes, with round tube, the nominal size is the same as the outer diameter. But with pipe, as you would think, the concern is with the volume of a fluid that could flow through it, so it is of lesser concern what the OD is.

Wall Thickness

Wall thickness for tube is given by it’s gauge, while the “schedule” of the pipe is the indication of its thickness. The higher the schedule, the thicker. But unlike the gauge of tube which is the same wall thickness for all tube sizes, the wall thickness of a pipe depends BOTH on it’s nominal size AND schedule. So a pipe the Schedule 40 in a 4″ Pipe will be a different wall thickness than a 6″ Pipe.

Click here for US Standard Pipe Sizes on Wikipedia

Clarification on Bollard Cover Sizes and Thicknesses

When we say a 6″ bollard cover, we mean that it fits a 6″ Pipe. Either 1/4″ or 1/8″ thicknesses in bollard covers will fit over the nominal pipe size as indicated.  

Metal tubes stored in a yard