Although 40 percent of us are falling short, it won't surprise you that it's true, on average, that most adults should aim for about eight hours of sleep, give or take an hour [source: Jones]. How much sleep we need varies based on age: If you're between age 18 and 64, for instance, your goal should be between seven and nine hours of sleep, and anyone over 65 should try for seven to eight hours.
Those who haven't reached adulthood yet need more than eight hours. Teenagers, for example, need eight to 10 hours, and kids ages 6 to 13 should be getting between nine and 11 hours per night. And when it comes to the little ones, we're looking at between 10 and 17 hours depending on age (3- to 5-year-olds need 10 to 13 hours; 1- to 2-year-olds need 11 to 14 hours; infants ages 4 to 11 months need 12 to 15 hours; and newborns, between 14 and 17 hours) [sources: NSF, Hischkowitz, et al].
It's important to remember, though, that the recommended guidelines may not be appropriate for everyone, and catching up with the sandman in small blocks throughout your day rather than spending the night with him might work out better for some people. Sleeping eight hours through the night is called monophasic sleep, but not everyone is a monophasic sleeper. Leonardo da Vinci, for example, is a famous example of a polyphasic sleeper, which means he slept in a few segments throughout the day rather than all at once. In fact, monophasic sleep cycles are a relatively new thing for humans, changing around the time that electricity became commonplace. Most animals are polyphasic sleepers, and historically humans were once naturally biphasic sleepers, meaning we slept for four hours, spent a few hours awake, and returned to sleep for another four hours [source: Campbell and Murphy].