The standard ranges
- Adults 18–64: 7 or more hours, commonly 7–9.
- Adults 65+: 7–8 hours.
- Teenagers: 8–10 hours.
- School-age children: 9–12 hours.
These come from consensus panels reviewing the evidence on health outcomes. They are useful as a sanity check and poor as an individual prescription.
How to find your own number
The most practical method is not a tracker. It is the sleep-extension test, done over a week when you have no obligations:
- Go to bed when you feel sleepy and do not set an alarm.
- Keep the same wake time naturally emerging for five to seven days.
- The average total sleep time once your system has paid off any debt is roughly your need.
Most people discover their number is somewhere between 7 and 8.5 hours, and that their weekday shortfall is real and cumulative — which is why weekend catch-up sleep feels so good.
Better measures than the clock
- Do you wake up without an alarm reasonably close to when you need to?
- Do you fall asleep within about 20 minutes most nights?
- Do you feel reasonably alert through the afternoon without caffeine rescue?
- Does one short night affect you mildly, or catastrophically?
If you are functioning well on six and a half hours consistently, you may be a genuine short sleeper — a real trait, with a genetic component, affecting a small minority. If you are functioning on six and a half by means of caffeine and willpower, you are not.
Why the eight-hour rule causes harm
Most people who become anxious about their sleep do so because of a number. They spend nine hours in bed to get eight hours of sleep, which fragments the night; they wake at 3am and calculate; they conclude the day is lost before it starts. That belief — that insufficient sleep predicts catastrophe — is one of the central maintaining factors in chronic insomnia, and it is one of the things CBT-I directly targets.
Also worth knowing: sleep need is not a debt that must be repaid hour for hour. See is six hours enough.
Quality matters as much as quantity
Understanding your sleep stages helps here: seven hours of consolidated sleep with normal cycling is better than nine hours of fragmented sleep. This is why sleep restriction can leave you sleeping fewer hours and feeling better.