Did you know that Pipe OD (Outside diameter) differs per pipe type. 4″ Copper tube has and OD of 4.125″. Steel/PVC pipe has an OD of 4.50″. Ductile Iron has an OD of 4.80″. How do you measure pipe OD accurately? Use an Outside Diameter Tape Measure. There are several different sizes we carry that you can chose from 24″, 36″ and 45″. The new 45″ unit we now carry can measure up to 42″ Steel/PVC/Ductile pipe.