Depends. Sometimes I only need like 3 hours sleep, if I've been feeling excited about something, like e.g. a new project. Sometimes I need even less, like a few seconds or minutes, if I've already been awake way too long, I guess because it makes me sleep in microsleep mode, which is like full blast sleeping. On a totally normal day, though, I don't know how much sleep I need because I always get way more than I need. (This wasn't the case at all back when I was going to school, or probably when I had a job either.) I seem to think it's around 8 hours, though.