In general, adults need between seven to eight hours of sleep, according to the National Sleep Foundation. However, sleep needs vary greatly based on a person's age, gender, physical condition and lifestyle.
The best thing to consider when it comes to the amount of sleep is how a person feels after having different amounts of sleep, according to the National Sleep Foundation. If a person feels tired after seven hours of sleep, but is happy and productive after eight, then eight hours of sleep is best. It is also important to pay attention to sleep debt in relation to sleep patterns. A person might have gotten enough sleep, but outside factors caused him to lose sleep in the days prior, causing him to still feel tired after getting enough sleep.