Many adults may think they're getting enough shut-eye, but in a major sleep study almost 80 percent of respondents admitted to not getting their prescribed amount of nightly rest. So, what exactly is the right amount of sleep? Research shows that adults need an average of seven to nine hours of sleep a night for optimal functionality. So, that talented dog doing back flips on the late night television might seem intriguing enough, but it's not worth your while if his canine acrobatics are cutting into your precious sleep time.