Basel watch show in Switzerland, largest watch show on Earth, indicate that the major high end manufacturers have, more or less, now "settled" on making watch cases in five distinct case diameters (or average diameters if the case is not round). They are: "micro, small, medium, large, and over-sized".
"Micro" refers to the traditional ladies size case of about 15-25 mm, small is 26-35 mm, medium is 36-42 mm, large is 43-50 mm, and over-sized is 51 mm and over. These are, of course, somewhat approximate ranges and what one manufacturer considers the largest of the medium cases it produces another manufacturer might consider to be the smallest of its own large size cases. I also note that there is a distinct trend toward removing any gender biases about the wearing of the various size catagories with the exception of the micro sized cases which are always intended for ladies. In other words, it's becoming "okay" for a guy to wear a "small" sized case IF he happens to have a small sized wrist and for a female to wear a "large" sized case if she prefers it even if it flops around a bit on her wrist. Removing this gender bias is also very good for a manufacturer's quarterly profits, of course!
Only a few years ago I was predicting that it wouldn't be too long before the over-sized catagory of watch case was phased out. But, it looks like I was wrong! Sales of these huge watches remain stable and, apparently, some guys like wearing a timepiece that weighs close to a pound and looks like the fuel gauge from a rocketship! I wonder, however, if this size catagory will still be popular, say, a decade from now.
My wrist is only 7 inches in perimeter and I find that if I wear a watch case any larger than about 42 mm in average diameter (which would be above the "medium" catagory of average case diameter), it starts to feel uncomfortable for me and look "too big" on my wrist. I can not even begin to imagine myself wearing a watch with a case in excess of 50 mm!