@sarah the answer to this question can't be given in figures. Sleep is meant to provide relaxation to our brain and body. Most of the body recovery from physical and mental stress is done while we sleep. The BRAIN on an average needs 5 hrs of sleep to optimal recovery whereas the requirement of BODY depends on person to person and kind of physical stress they go through , so it can be from 6~8 hrs a day. Also sleep is dependent on age too.. so, what is said for adults. 😁