Sleep Quantity vs. Sleep Quality: Which One Makes the Biggest Difference?

Sleep can be a confusing thing. Some days, you're so tired you wish your bed would swallow you whole despite sleeping for 9 hours. But on other days, you wake up ready to tackle the day after sleeping for 7 hours.

So, what's the deal? It's unclear on the surface, but dig into the research, and you'll find that two primary factors determine how well you sleep: sleep quantity and sleep quality.

Read this article to learn more about each and understand which one is more important for improving your sleep health.

Key Takeaways

• Sleep quantity refers to the number of hours you spend asleep, while sleep quality is how well you sleep. Achieving a balance between both is vital for better sleep health.

• Poor sleep quality and quantity can lead to various physical and mental health issues.

• Improving sleep quality and quantity involves adjusting your lifestyle and cultivating healthy sleep habits.

Table of Contents

• What Is Sleep Quantity?

• What Is Sleep Quality?

• Sleep Quantity vs. Quality: Which Is More Important?

• What Issues Can Poor Sleep Quality Cause?

• How to Improve Sleep Quality and Quantity

• Conclusion

• Frequently Asked Questions About Sleep Quantity and Quality

What Is Sleep Quantity?

Sleep quantity is defined as the number of hours of sleep required to fully restore your energy. The Journal of Clinical Sleep Medicine says 7 to 9 hours is the ideal sleep quantity for adults aged 18 to 64.⁽¹⁾

However, how much sleep you need to function properly may vary depending on your age, lifestyle choices and overall health.

According to the Mayo Clinic, the number of hours differs per age group⁽²⁾:

• Including naps, infants (ages 4 to 12 months) require 12 to 16 hours per 24 hours.

• Toddlers (1 to 2 years) require 11 to 14 hours of sleep per 24 hours, including naps.

• Preschoolers (3 to 5 years) need 10 to 13 hours of sleep per 24 hours, including naps.

• Children (6 to 12 years) require 9 to 12 hours per 24 hours.

• Adolescents (13 to 18 years) need 8 to 10 hours per 24 hours.

• A healthy adult requires a minimum of 7 hours of sleep every night.

Consider these questions when determining the correct sleep quantity for yourself:

If you're not feeling ready to get up and go after 7 hours of sleep, your sleep quantity may be to blame. Try getting more sleep, but stick to less than 9 hours.

If you're not ready to get out of bed after 9 hours, prioritize working on the quality of your sleep instead.

What Is Sleep Quality?

Sleep quality refers to how well you sleep. Life Hack says one way to wake up feeling rested is to get as much REM sleep as possible.⁽³⁾ The REM sleep stage is the phase wherein you dream. It's crucial for memory consolidation, cognitive functioning and emotional regulation. You need to enter and spend adequate time in this sleep stage for quality sleep.

Measuring sleep quality is more complicated than determining your ideal sleep quantity. Sleep quality measures include the following:

• Sleep onset latency refers to how quickly you can fall asleep. You should be able to do so within 20 to 30 minutes.

• Sleep efficiency is the ratio of time you actually spend sleeping compared to how much time you spend in bed. Eighty-five percent is considered the minimum.

• Sleep duration refers to the total amount of time you spend sleeping. We mentioned earlier that adults need at least 7 hours of sleep every night.

• Awakenings are how many times you wake up at night after falling asleep. More than once, and your sleep quality may be affected.

• Wake after sleep onset (WASO) is how long it takes for you to fall back asleep after waking up. It should take you no more than 20 minutes.

If you have difficulty meeting any of the above benchmarks, then poor sleep quality is likely the primary reason you're having trouble sleeping.

Underlying health problems can negatively impact sleep quality. Sleep disorders like insomnia or sleep apnea prevent you from drifting off and staying asleep. Mental health issues, such as bipolar disorder or depression, are also potential culprits. Indigestion, nocturia and chronic pain can also harm your sleep quality.

These conditions can create a vicious cycle, where the condition becomes both a symptom and a cause of sleep deprivation. It's important to consult a healthcare provider to identify the root problem so they can prescribe the proper treatment.

Sleep Quantity vs. Quality: Which Is More Important?

You may need more help in one area than the other, but the perfect formula for healthy sleep combines both sleep quality and quantity.

Without the proper quantity of sleep, you'll fail to function. However, adequate sleep quantity combined with poor sleep quality will still leave you exhausted and impact your alertness during the day.

Insufficient sleep leads to sleep deprivation. Poor sleep quality increases your risk of health issues like heart problems, type 2 diabetes, depression and obesity.

What Issues Can Poor Sleep Quality Cause?

Poor sleep quality negatively impacts your physical and mental health. Here are several issues it can cause:

• It can cause difficulty concentrating and solving problems. Plus, it can also impair your memory.

• It can increase your risk for certain mood disorders, such as depression and anxiety, and it can also make you more irritable.

• You may get sick more often, as poor sleep quality can also weaken your immune system.

• It can upset the balance of appetite-regulating hormones, causing you to overeat and consequently gain weight.

• It puts you at a higher risk for serious chronic conditions, like heart disease, high blood pressure and diabetes.

• You'll feel more tired because of a lack of energy and endurance.

• It increases your risk of accidents because poor sleep quality reduces alertness and reaction times.

How to Improve Sleep Quality and Quantity

If you want to improve your sleep quality and quantity (and you should), here are six tips to help you do it:

Tip #1: Get Quality Sleep by Making Changes to Your Bedroom

Establish a good sleep environment in your room by making it quiet, dark and cool. These conditions will make it easier to drift off at the appointed time every night. Maintaining a regular sleep schedule is a sleep hygiene habit that regulates your internal body clock.

Use a white noise machine to counter ambient noise. Heavy curtains or an excellent sleep mask can block the light and help you fall asleep faster. As for your room's temperature, keep it between 60 and 75 degrees Fahrenheit.

Another way to ensure you have a good sleep environment is to keep your electronic devices and work materials outside the bedroom. Removing these work-related items will help you associate your room with rest and nothing else.

Tip #2: Only Hit the Sack When Sleepiness Sets in

If your sleep latency is long (you aren't asleep within 20 to 30 minutes of lying down), then leave your bed and do something that relaxes you in another room.

For instance, you can play calming music or read a book until you're sleepy or tired. Keep the lights dim to avoid messing up your internal clock. For similar reasons, avoid noisy areas and electronic devices.

Tip #3: Take Naps Before 5 in the Afternoon

If you must nap, do so before 5 p.m. Keep it short to avoid affecting your sleep quality and quantity.

Tip #4: Add Exercise to Your Routine

Exercising for even 10 minutes a day can positively impact the quantity and quality of your sleep. It can also reduce the risk of developing sleep disorders, like sleep apnea.

Just make sure to exercise at least 3 hours before you sleep. Exercise stimulates your body, which will make falling asleep more difficult. Plus, your adrenaline levels and body temperature will increase, which doesn’t promote relaxation either.

Tip #5: Start Documenting Your Sleep

Maintain a sleep log. Every evening and morning, jot down your bedtime, wake time, duration of your sleep and the number of times you woke up.

You can also include the activities you did throughout the day and the foods you ate to determine how they affect your sleep.

You or the sleep medicine professional with whom you share this log may be able to determine which factors improve or compromise your sleep quality.

Consider a professional sleep assessment to identify sleep disorders like periodic limb movement, sleep apnea, narcolepsy, restless legs syndrome and insomnia, among others. You'll likely undergo a sleep study for a proper medical diagnosis and tailored advice.

Tip #6: Consider Lifestyle Changes to Achieve High Quality Sleep

Consider adjusting your eating habits to achieve good quality sleep. Knowing what to eat or not eat before bedtime is key. For example, almonds contain sleep-promoting tryptophan and magnesium, while spicy and fatty foods can cause indigestion. Avoiding big meals before bedtime can also help you sleep better.

Steer clear of alcohol and caffeine too close to bedtime as well. Caffeine can make it difficult to fall asleep at night, while alcohol can cause frequent awakenings, leading to poor sleep quality.

Conclusion

Sleep quantity and quality are inextricably linked. Improve your sleep health by optimizing the amount of time you sleep and the factors that impact the quality of your sleep.

Remember to get 7 to 9 hours of sleep at night and ensure you meet the measures of good sleep quality, namely: sleep efficiency, sleep onset latency, sleep duration, awakenings and wake after sleep onset. The tips we mentioned above should help you improve your sleep health.

Which of our sleep optimization tips helped you get a good night's sleep? Did we miss any of your go-to strategies? Let us know by leaving a comment below.

Frequently Asked Questions About Sleep Quantity and Quality

Can I Make Up for Poor Quality Sleep by Sleeping Longer?

Sleeping longer may help alleviate the fatigue associated with sleep deprivation and boost alertness, but it will not make up for poor-quality sleep. You need adequate sleep to cycle through all sleep stages, including REM and deep sleep, to boost sleep quality.

How Do I Know I Am Getting Quality Sleep?

You know that you're getting quality sleep when you sleep 7 to 9 hours at night, and it takes you within 20 to 30 minutes to drift off. You also sleep through the night, and if you don't, you wake up only once. You wake up well-rested and energized, and you also experience little to no daytime drowsiness and fatigue.

Is It More Important to Have a Consistent Sleep Schedule or to Sleep Enough Hours in the Night?

It is equally important to have a consistent sleep schedule and get enough sleep at night. Maintaining a consistent sleep schedule regulates your body's circadian rhythm, helping you fall asleep faster and stay asleep throughout the night (which is called sleep continuity).

Meanwhile, getting enough sleep at night allows you to cycle through all the sleep stages, including REM and deep sleep, which are essential for physical and mental recovery.

Why Do I Still Feel Tired After Sleeping 8 Hours During the Night?

There are several reasons you might still feel tired after sleeping 8 hours at night. Health conditions, such as sleep disorders (insomnia, sleep apnea), mental health issues (depression) and chronic conditions (chronic fatigue syndrome), can cause sleep disruptions, resulting in next-day fatigue.

An inconsistent sleep schedule can also disrupt your body's internal clock, affecting your sleep patterns and compromising your quality of sleep. These, in turn, make you feel tired when you wake up.

Stress and anxiety can also affect how well-rested you feel, regardless of how long you slept the night before. Poor lifestyle habits, such as an unhealthy diet, excessive screen time too close to bed, and a lack of exercise, are also known to cause fatigue.

Sources:  

(1) "Recommended Amount of Sleep for a Healthy Adult: A Joint Consensus Statement of the American Academy of Sleep Medicine and Sleep Research Society." Journal of Clinical Sleep Medicine, jcsm.aasm.org/doi/10.5664/jcsm.4758. Accessed 24 September 2025.

(2) "How many hours of sleep are enough for good health?" Mayo Clinic, www.mayoclinic.org/healthy-lifestyle/adult-health/expert-answers/how-many-hours-of-sleep-are-enough/faq-20057898. Accessed 09 September 2025.

(3) “Quality or Quantity? Why Don’t You Sleep On It." Lifehack, www.lifehack.org/643556/quality-or-quantity-why-dont-you-sleep-on-it. Accessed 25 March 2024.