•Toddlers need 11 hours of sleep every night, plus a two-hour nap during the day.
•Preschoolers need 11 to 12 hours of sleep a night.
•School-age children need 10 hours of sleep each night.
•Teens need 9.25 hours of sleep every night. Most get less than 8.5.
•Adults need about 8 hours of sleep every night. To determine exactly how much sleep you need - on a night you feel fairly rested, sleep until you wake up on your own. Feel rested? The length of the time you slept is how much sleep you need.
If you get one hour less sleep than you need each night for eight nights in a row, your brain will need sleep as desperately as if you had stayed up all night.
Source: William Dement, Stanford University Sleep Researcher