I suspect in any case that when the term "beer-can thick" is used seriously, what is being claimed is just that the cock is as wide as the diameter of a beer can, not that it has the same circumference. For instance, I could claim that my cock is "as thick as a can of Gillette shaving cream" on the strength of its being as wide as such a can (
photo), even though the can has a much greater circumference--6.7 inches as against my cock's 6.3. I measured a pint can of Boddington's with a tape and found it to be 8.25 inches in circumference, which implies a diameter of 2.6 inches. I can believe that some people posting on this thread have seen cocks that wide; that is not to say that they were 8.25 inches around.