Scientifically it has been observed that we need at least 5 Hours of sleep to completely rejuvenate our body and muscles.

The age old belief is that we need 8 Hours of sleep to live a healthy life.

It also depends upon what age group you belong to infants need the most sleep. Teenagers also require to sleep for 10 hours. Adults after the age of 18 years require less sleep.

In my opinion you may sleep till the time you are completely fresh. When you get up from your bed there should be no laziness or no feeling that you want to sleep more. There is no point in being awake and not being productive at the work you do. A sharp mind can accomplish more than a sleepy mind in the same time interval.