Every person is different and will require different amounts of sleep to run on all eight cylinders (see, I didn’t say four cylinders). The need for sleep generally follows a bell curve: a few people can get by perfectly fine on as little as 4 to 6 hours of sleep (some folks actually have a genetic variation that gives them more intense sleep sessions, which allows them to get by on less); the vast majority of people need 7 to 8 hours; and a few need as much as 9 to 10 hours of sleep.

via What Every Man Should Know About Sleep | The Art of Manliness.