How many hours of sleep do people need every night?

In my opinion, it depends on the person. Someone needs six hours for sleeping and the other person needs ten hours. A lot of scientists suppose that adults needs from seven to eight hours for sleeping in average. But, of course, children under the age of 18 need more time. For example, babies under the age of 5 need almostly 12 hours! There is hypothesis that how many hours you need depends on the time when you sleep. For example, from 11 p.m to 12 p.m one hour of sleeping is equated to three hours. But from my point of view you should choose by yourself when and how much you should sleep and also you should remember to keep the day.