If i go to bed before 12am, ineed a 8-hour sleep. If later than that, i will probably have aheadache.

it also depends on your age but the best is from 6 to 8h and you should study sleep way properly.my english skill is not good ^^

7-8hr is the best.

me？.....i guess its 6-10/11

Thank you all. Sometimes I was extremely tired but can't sleep.