I believe that 7 or over puts the said person in the 'big' category.
With that being said, some women prefer size to the most extreme they can find/tolerate.
Of course we all know women are rather bad at being able to judge penis size. I've had 2 exes that swore up and down they were with a guy that 8.5 and 9.
Both of which stated I was bigger, then I measured for them by request as they didn't believe me when I said what my size was.