Conventional thinking is that the average healthy adult needs around 8 hours sleep per night. In reality, people need the amount of sleep that they can function best at. Some people function great with only 5 hours of sleep per night while others may need 10 or more. In addition, sleep needs can vary throughout a single persons lifetime for various reasons including, age, health, and stress levels, among others.
Lately, I have been functioning on less than 5-6 hours of sleep, but I feel more rested with 7-8 hours.