Getting a solid eight hours of uninterrupted sleep has long been seen as the gold standard of a good night’s rest. While that is a fine sleep target to aim for, I’ve spent the past year tracking and analyzing my sleep with the best sleep trackers on the market — and I’ve found total sleep time shouldn’t be your main focus.
Lately, I’ve noticed that no matter my total sleep time, be it around the prime seven and a half to eight hours, or longer, my sleep score is never in the ‘good’ range (above 70, according to Oura Ring). The only thing that pushes my score up is if I spend plenty of time in two essential sleep stages: deep sleep and REM sleep.
Sleep quality vs sleep quantity
It’s easy to feel cheated when you wake up from eight hours sleep feeling unrested and with a subpar sleep score. But science increasingly shows sleep quality is more important than quantity.
This means, while total sleep time is a helpful baseline for getting enough rest, the composition of that sleep – specifically the time spent in restorative stages – is what actually influences physical recovery and mental clarity.
The quality vs quantity debate has long been a grey area when it comes to sleep. But research indicates that we should aim to achieve healthy sleep architecture, i.e. good quality sleep, rather than hit a certain sleep duration.
Now, I’m well aware that I shouldn’t take my Oura Ring sleep report as gospel, and perceived sleep quality and actual energy levels provide a good indicator of how well you slept without tech intervening. But, as one of the most accurate commercial sleep trackers you can buy, according to both our testing rubric and scientific studies, it’s interesting to look into how the Oura Ring grades sleep.
These two sleep reports from two different night’s sleep support the narrative that sleep quality is more important than quantity.
As you can see in the above data, even when I slept ten minutes over the idealised eight hours, my sleep score was lower than when I slept just 6 and a half hours. That’s because I didn’t get enough deep and REM sleep.
But how much is ‘enough’?
Ideally, adults should aim for 1.5 to 2 hours of deep sleep per night, assuming a sleep duration of between seven to nine hours. But that amount depends on total sleep time. According to studies, 13% to 25% of your night should be spent in deep sleep for optimal recovery. Hence, my 38 minutes, accounting for 8% of the night, didn’t cut it.
Sleep scores are beginning to reflect that quality dimension, not just totals
Ariel Garten, neuroscientist and Muse co-founder
When it comes to REM sleep, experts say between 1 hour 45 minutes and 2 hours 15 minutes is a healthy dose — that equals around one quarter of the night. Again, just 1 hour 1 minute was not enough on my particular night of poor quality sleep.
“Sleep scores are beginning to reflect that quality dimension, not just totals,” explains Garten.
Hence my relatively low score. Wade adds: “Sleep trackers focus on deep and REM sleep because these stages are when your body and brain do the most important repair work. If you sleep a long time but miss enough deep or REM sleep, your restorative processes are limited, and your score reflects that.”
What does quality sleep look like?
A healthy night’s sleep is one where you cycle through the four essential sleep stages. This means spending ample time in the two stages of light sleep (NREM1 and NREM2), deep sleep, and REM sleep, forming a full sleep cycle.
Garten, who studied neuroscience at the University of Toronto and founded Muse sleep headbands, says quality sleep is defined by “smooth transitions between light, deep, and REM stages” and “minimal fragmentation across the night” because it is the structure and continuity of sleep that drive how refreshed you feel upon waking.
The importance of deep sleep
In a nut shell, deep sleep promotes repair of muscle tissues, regenerates cells in the body, improves immune function, and flushes toxins from the brain. In a healthy sleep cycle, you get the most deep sleep in the first half of the night and REM sleep comes after.
Board-certified internist Dr. La Puma explains: “Deep sleep concentrates in the first half of the night. If you stay up until 2 AM, you don’t just shift your sleep later: you miss the deep sleep window entirely, because your body clock is programmed to reduce it as morning approaches. You can’t get it back by sleeping in.”
However, Garten points out that it is increasingly clear from research that this deep sleep must be stable. She says: “In deep sleep specifically, quality means slow-wave activity occurring in sustained, continuous ‘trains.’ These organized bursts of slow waves reflect coordinated brain recovery. When those trains are fragmented (stopping and starting), sleep can feel less restorative even if total deep sleep minutes look normal.”
Ultimately, if you cut sleep short, or fragment it, your brain doesn’t complete its cleaning cycle. “During deep slow-wave sleep, your brain cells physically shrink by up to 60%,” explains Dr. La Puma. “That opens channels between them, and cerebrospinal fluid rushes through like a power wash, flushing out metabolic waste — including beta-amyloid, the protein that accumulates in Alzheimer’s disease,” he adds.
The importance of REM sleep
REM sleep is essential for creativity, information processing, emotional regulation, and memory consolidation. Your brain is most active during this sleep stage and it enables you to process the emotional weight of the day — it’s also usually when dreams occur.
Ever wake up feeling mentally foggy or emotionally sensitive? That morning grogginess is likely due to lost REM sleep. Dr. La Puma, who has researched how modern indoor living disrupts sleep architecture for his upcoming book Indoor Epidemic, explains:
“REM is heavily controlled by your circadian rhythm and concentrates in the second half of the night. If your alarm cuts your sleep short by even 30 to 45 minutes, you’re disproportionately losing REM, not light sleep. That’s why you wake up groggy and emotionally reactive. You didn’t just lose sleep. You lost the specific stage that regulates your mood.”
That doesn’t mean light sleep isn’t crucial, too, Garten clarifies. “Light sleep isn’t ‘bad’ sleep — it’s necessary scaffolding,” she says. “But the restorative payoff comes when the brain successfully enters and sustains deep and REM phases. Sleep is cyclical. The brain needs lighter stages to re-enter deeper recovery states throughout the night.”
How to increase your REM and deep sleep
Now for the question that’s probably lingering in your mind: Can you actually do anything to get more deep and REM sleep?
The good news is, according to experts, there’s plenty of habits you can follow and environmental factors you can adapt to better your chances of getting that all-important deep and REM sleep.
Get morning sunlight
Multiple studies show that a quality night’s sleep begins as soon as you wake up — and Dr. La Puma agrees.
“Get 15 minutes of outdoor light within an hour of waking. Not through a window, because glass filters the wavelengths your brain needs,” advises the doctor of internal medicine. “This signal hits your master clock and starts a 12 to 14 hour countdown to melatonin release. Skip the morning light, and your brain doesn’t know when to start producing melatonin that night.” Clever, huh?
The sleep hormone melatonin tells your body and brain it’s time to wind down. This makes it easier to fall asleep without tossing and turning, enter those essential deep sleep stages, and maintain continuous sleep cycles through the night.
Sleep in a cool room
There is a close connection between sleep and temperature, and it’s not about cosying up in thick blankets and fluffy pjs. It’s quite the opposite.
Science shows sleeping at a cool temperature helps you get better quality sleep. La Puma says: “Your core body temperature needs to drop 2 to 3 degrees Fahrenheit to trigger deep sleep. Keep the bedroom between 60 to 67 F.”
A cool bedroom aids this thermoregulation, promoting the release of sleep hormones and preventing overheating which causes shallow sleep and nighttime awakenings.
Go to bed and wake up at the same time every day
Regulating your circadian rhythm is one of the easiest ways to become a great sleeper. When you go to sleep and wake up at the same time night in, night out your body gets used to releasing the hormones you need to sleep at consistent times.
When your body clock is regulated, you’re more likely to fall into deep sleep and seamlessly move through sleep cycles, so you clock up that all-important REM sleep too.
Understandably, a late night is unavoidable sometimes. In this case, waking up at your usual time, even if it means making your night sleep shorter, is better than throwing your rhythm off entirely.
The bottom line: Instead of panicking over fitting in eight hours sleep into your already busy schedule, experts recommend practising simple healthy sleep habits to promote the quality of the sleep you get, be that eight hours or less.
