Different people have different sleep needs. In addition, the number of sleep hours a person requires varies according to genetics, chronotype, and significant life stages. But there is a straightforward way to calculate the amount of sleep you need to feel rested and productive at any given time.
The Magic Number
As we head into Autumn, many of us experience a change in our sleep patterns: we start sleeping less or more while our body adjusts to the new season. But what is a good number of hours of sleep per night? You have undoubtedly heard that adults need about 8 hours of sleep daily. While this can be true for some, a more accurate magic number may fall within the range of 7 to 9 hours of sleep for most people and may well be outside these limits for a few others. I’ve been a 6.5-hour sleeper almost all my adult life, but my daughter – now well into her 20s – needs a good 8.5 hours of sleep to feel refreshed and function well the next day. Everybody is different.
Your Sleep Drive
In the same way, you have a hunger drive that tells you to eat when you’re hungry; you also have a genetically predetermined sleep drive that makes you want to go to sleep when you’re tired. Your sleep drive also determines the rate you can fall asleep and the length of your sleep cycles. In general, most people go through five 90-minute sleep cycles per night. That is why the average person needs about 7.5 hours of sleep (five cycles of 90 minutes each works out to be 450 minutes in total, which is the equivalent of 7.5 hours). However, some people’s cycles are longer or shorter.
Calculate Your Individual Sleep Drive
A good place to start is to take the 7.5 hours as a base and start from there. Check the time you usually wake up and count back 7.5 hours. So if you typically wake up at 7:00 am, you would need to go to bed at 11:30 pm to get 7.5 hours of sleep. Make it a point to go to bed at 11:30 pm for at least ten days. By the end of this period, if you start waking up before your alarm clock or immediately with your alarm clock without the need to snooze, then this would be your ideal amount of sleep. If you still have difficulty waking up with your alarm, try going to bed half an hour earlier, at 11:00 pm. Keep moving your bedtime up by 30 minutes until you wake up just before your alarm. The number of hours you end up with is how much your body needs. This is your natural sleep drive.
The Role Of Chronotype
Unfortunately, more than 50% of people won’t be able to go to sleep much earlier to ensure the five cycles of 90 minutes. This is due to their chronotype – their internal biological clock that determines if they are a “night owl” or an “early bird,” for example. People who sleep late or wake up early need to modify their lifestyle according to their chronotype to fit enough hours of sleep to complete all required cycles. In practical terms, if you usually go to bed at 1:00 am, you need to make lifestyle changes that allow you to wake up around 8:30 am, given your sleep drive is 7.5 hours. Otherwise, you would be going into a constant sleep-deprivation state, which will be detrimental to both your physical and mental health and negatively impact your mood, productivity, and many other aspects of your life.
In Summary
• Sleep Drive: Figure out exactly how much sleep you need every night and ensure you go to sleep at a time that allows you to sleep through the five cycles.
• Chronotype: Respect your internal biological clock and adjust your lifestyle to allow you to sleep the complete five cycles.
“I love to sleep. Do you? Isn’t it great? It really is the best of both worlds. You get to be alive and unconscious.” — Rita Rudner, American Comedian
