Sleep duration refers to the total amount of time a person spends asleep over a given period, typically measured per night. It is one of the key dimensions of sleep health, alongside sleep quality, sleep timing, and regularity. Sleep needs vary across the lifespan. Newborns require 14 to 17 hours of sleep per day, while toddlers and young children need 10 to 14 hours. School-age children typically need 9 to 11 hours, and teenagers need around 8 to 10 hours. Most adults function best with 7 to 9 hours of sleep per night, while older adults may need slightly less, around 7 to 8 hours. Both insufficient sleep duration and excessive sleep duration can have negative health consequences. Chronic short sleep — regularly sleeping fewer than 7 hours per night — is associated with increased risk of obesity, cardiovascular disease, type 2 diabetes, impaired immune function, mental health disorders, and reduced cognitive performance. Conversely, consistently sleeping more than 9 hours may be associated with underlying health conditions such as depression or chronic illness. Individual sleep needs can vary due to genetics, health status, activity level, and other factors. The best indicator of adequate sleep duration is how you feel during the day — if you feel alert, energized, and mentally clear without needing a daytime nap or stimulants like caffeine, you are likely getting enough sleep. To support optimal sleep duration, maintain a consistent sleep schedule, create a comfortable sleep environment, and adopt healthy sleep habits. If you consistently sleep for adequate hours but still feel unrested, the quality of your sleep may be the issue rather than its duration.