Most people survive with 8 hours of sleep, some need 10, while a very small minority need only 6 hours of rest every night. But how do we figure out our optimal sleep hours? The number of hours of sleep we need to wake up without an alarm clock.
First you need to create your own sleep clinic. Clear out all nighttime agenda for a weekend. On Friday night, go to sleep at your usual sleep time and the next morning, wake up naturally. You shouldn't count this as your optimal sleep as you are probably making up for the weekday sleep deprivation. Go to sleep on Sat night again at your regular time and wake up naturally on Sun morning. That is the amount of hours of sleep you need to function best.
That is your optimal sleep level.