I don't know my wrist size exactly, and the SA at the store said it didn't really matter. I know its personal preference, I see a lot of people prefer the snug fit to lose and vice versa but the 16 is lose enough where I have a little room. I can turn the 16 on my wrist with some effort while the 17 does not turn on it's own but turns easily. When I went to the store the first time I chose the 16 and went home thinking about the 17 and what could be. I constantly have to change my watch size/bands when I retain water or gain/lose weight, that's whats worrying me and I always want to be able to wear it.