Don't know really.. 12-14 maybe it depends. I try not to sleep too late though or it'd mess up schedule real hard unless there's a real good late movie I wanna watch.
Usually 14 hours on a weekday, and between 10 and 15 hours on a weekend, because I wake up/go to sleep and a much larger range of times on the weekend. (Basically whenever I feel like it because I don't have school to go to or as many chores to do.)