In the plumbing trade the size of copper tubing is measured by its
nominal diameter (average inside diameter). Some trades, heating
and cooling technicians for instance, use the outside diameter
(OD) to designate copper tube sizes. The OD of copper tube is
always 1/8th inch larger than its nominal size. Therefore, 1"
nominal copper tube and 1-1/8th" inch ACR tube are exactly the
same tube with different size designations. The wall thickness of
the tube, as mentioned above, never affects the sizing of the
tube. Type K 1/2" nominal tube, is the same size as Type L 1/2"
nominal tube (5/8" ACR).
