Let's be sure we don't make the common mistake of misunderstanding the words "diameter" and "circumference." I have a cigar video made by one of the world's biggest companies, and starring a Cuban expatriat topflight cigar maker, executive and industry personality. Even in this video, the incorrect term "circumference" is given as ring size.
As one poster correctly observed, "diameter" is the correct term for ring size, but diameter is NOT the "size around" of the cigar. Ring size, or diameter is size ACROSS. A ring size of 48, found on many Churchill sized cigars, means 3/4 of an inch, because ring size goes according to 64th's of an inch. A cigar with a ring gauge of 64 means it measures exactly one inch across the widest point of the cigar.