Anything above an 8.5 is all about appealing to all of a guy's individual little preferences.
If you are talking about looks, she has to be exceptional from head to toe. She has to be beautiful, with a body to match, that a nine- ten. If you are talking about overall, then she has to have a great personality and a head on her shoulders etc. along with being exceptional physically. 7-8 are basic cute or pretty girls with nice bodies with good personalities they are what most guys want and go for.
What Girls Said 1
it is subjective but I don't think a 10 really exists. then again I am picky.
a girl who is a 10 would have to be flawless. perfect body and perfectly gorgeous face. she can't have imperfections like zits or dark circles. she has to always look put together, made up but not obnoxiously so, dressed impeccably from head to toe, etc, because a 10 just "stuns" and part of that is maintenance.
perfect features. perfect face shape, nose, eye shape, no dark circles, perfect brows, smooth creamy skin, long smooth shiny hair that is not too curly or flat or frizzy. perfect body. curves in all the right places, but not obnoxiously so. not too skinny or scrawny either. perfect teeth and smile. perfect lips.