As Amy has said, about 10 hours! However, some people do not need as much sleep and so it is just a guideline. If you sleep, say, 7 hours when all is well with diet, stress levels and general routine, then you need not force out another 3. But do try to sleep young one.
If I get under 7 hours, I'm tired. If I get over 9 hours, I feel well rested the NEXT day, I feel sluggish that day.
you don't need 10...most research has shown that teenagers need 8-9 hours, but with the demands of school and other "obligatory" bull****, most kids can't manage that, and thus make up for it on the weekend, like you. how you feel is relative though. sometimes I feel fine on 5 and drowsy on 8, it just depends.
And telling it is that they get more sleep at weekends, hmm! Mind you, I have never been so good at taking my own advice. To control stress levels is very important but not easy.