I have a 6.5" wrist and I'm really loving 43mm.
I find most small watches a bit boring.
I might even like up to 45mm if the lug to lug is under 50mm - but I've never tried one.
Fun fact. A 6.5 inch wrist is the most common wrist size in the watch community.
Ha ha! Got 6.5 too. And wear a 45. Looks all right in the mirror; my personal rule is y'gotta still be able to see the band on both sides.
I have a 7" wrist and prefer 40mm or under mostly. My 41mm GSAR is about as big as I like to go.
I like watches of all sizes, but feel that 39-41mm is ideal for my 17cm (6.75") wrist. Of course, other factors come into play as well, such as lug-to-lug distance, height, bezel size, dial color, etc. The largest watch I have is a 46mm Hamilton Khaki Pilot, which is a bit too large for me, but is actually quite comfortable to wear.
My wrist is also 17cm (6.75") I made a rule that 50 lug to lug is max (if a watch is more it is cut) and divers or sport watches with wide bezel are okay up to 43, aviators up to 41, field and dress up to 40. 34 is the smallest to wear.
I have a 6.75" wrist, and I find 42mm is usually the max for me (with exceptions here and there). But I've been gravitating to smaller watches lately, 36-40mm.
Like @witcher.watcher and @tempus I have a perfectly sized wrist. 50mm lug to lug is about as big as fits well, although 48mm usually fits better.
I think that we undervalue smaller watches. For example:
This is a mere 30mm. It has little to no bezel, so it is all dial. In fact, I have several 38mm watches with the same size dial. It is comfortable and easy to read. And it is not boring.
6.75". I'm good anywhere between 34 and 48mm, as long as the lugs are well under 50mm and the crown isn't jabby.
My smallest watch is also a 30mm (well actually 30.8), and I think it works great on my wrist. Lug to lug is only 36.4mm, and thickness is a mere 5.4mm. I know that this watch is scorned by many enthusiasts as being a fashion watch, but I think it looks killer.
I have a 7.5" wrist and I wear from 32mm to 50m.
WWII era 32mm Bulova military watch
50mm Pro Trek PRW2500
As @Aurelian and others have pointed out, it is not just case diameter that determines wearability. Lug-to-lug, dial size, lug turn down, and bezel thickness all impact how a watch fits on a wrist. My 50mm Pro Trek fits my wrist better than the 45mm Bulova Lunar Pilot, which has a completely flat case. My 34mm Timex Marlin looks bigger on my wrist than my former 38mm SKX013. Of course, both fit and look are subjective, and these are my opinions on fit and look. 😄
A 41 mm wears very comfortable on my 7 1/2" wrist. Not all of us posses that certain style that it takes to rock oversized watches.
I love that Bulova (It seems I am a sucker for "field/military" watches the more I delve into the watch world)
Got a 7 1/4“ wrist. This big boy tries his best. Gotta cinch it up.
This is a good one when I need to speed out to Tashi Station for some power converters.
8.25" wrist and I'm really considering getting a 55mm or 65mm flieger just as a funny watch.
Awesome reference, I must say