Quick answer
Start around 18–20°C (65–68°F)
- Most adults
- Around 18–20°C is a sensible starting range. Current sleep-organisation guidance centres on 65–68°F, not the 16°C end of older advice.
- It is a range, not a target
- 18°C is the cool end. Many people sleep more comfortably at 19–21°C, and choosing that is not a mistake.
- Why not colder
- 16°C (61°F) sits at the cold edge — fine for some people, uncomfortable for many, and not well supported as an ideal.
- If you run warm
- Try a lighter duvet and moving air before you drop the room further.
- If you run cold
- Raise the room a little and add a layer on the bed rather than overheating the whole room.
- Measure it
- Use a cheap digital thermometer at mattress height, not a wall thermostat across the room.
What the evidence actually shows
The honest answer is that there is no single magic number, and the research is looser than the confident figures you see online. What it does support is a clear direction: a cool, dark and well-aired room helps, and heat is the better-established problem. If you are tuning the whole bedroom, pair this guide with our advice on darkening a room without sealing it up and on why humidity matters as much as temperature.
Two sources are worth separating, because they answer slightly different questions:
- Comfort guidance. The Sleep Foundation's current guidance (updated July 2025) puts the best temperature at about 65°F (18.3°C) and says most doctors recommend keeping the thermostat between 65 and 68°F (18–20°C).
- Measured sleep quality. A 2023 study in Science of the Total Environment tracked older adults at home with wearable sleep monitors and bedroom temperature sensors. Sleep was most efficient and restful when the nighttime temperature sat between 20°C and 25°C, and sleep efficiency fell by a clinically relevant 5–10% when the room rose from 25°C to 30°C.
Two things stand out. First, the measured-study range is warmer than the 16–19°C figure that circulates widely — closer to 20°C and above, not below it. Second, the relationship is non-linear and varies a lot between people, so any single number is a starting point, not a rule.
"Best for sleep" is not the same as "most comfortable"
The ranges above describe the conditions most often linked to good sleep. They are not a claim about the temperature you would choose to sit in. Comfort depends on your bedding, nightwear, humidity, air movement, age and body, which is why two people can disagree about the same room. If 18°C feels cold to you, 20–21°C is a perfectly reasonable place to sleep.
This is comfort guidance, not medical advice
Sleep needs differ with age, health and medication, and the strongest constant-temperature study above looked specifically at older adults. If you have a sleep or health condition, follow the advice of your own clinician rather than a general guide.
Why you keep seeing 16–19°C quoted
The figure comes from older US guidance that described a comfortable range of roughly 60–67°F, which converts to about 15.6–19.4°C. Once published, that range was copied from site to site and hardened into an apparent fact — which is exactly why it turns up so often, and why it now looks colder than the guidance it came from.
Current sleep guidance has drifted slightly warmer at the bottom end: 65°F rather than 60°F as the recommended floor. So treat 16°C as the cold edge of a broad range, not a target to aim for. If your room sits at 16°C and you sleep well, that is fine; if you are cold and restless, the number is not something you need to endure.
One practical correction: check the date and the address of any page you cite. Guidance pages get revised and moved, and a recommendation can quietly change while the number in an old article stays frozen.
How to find your own number
Start from 18–20°C and adjust one degree at a time, because the right number is the one that keeps you comfortable — not the one a chart prefers.
- Place a digital thermometer at mattress height. On the nightstand beside the pillow is close enough.
- Read it after the room has settled. Give it an hour or two after heating, cooling or opening a window.
- Check again at 3 a.m. Many rooms drift warmer or colder once the heating cycles off, and the second half of the night is when heat tends to build up.
- Note humidity at the same time. A dry or damp room changes how the same temperature feels — see why the bedroom feels damp in the morning.
Adjust the bed before the room
Changing a duvet or a layer of bedding is faster and more energy-efficient than heating or cooling the entire bedroom. Reserve room-level changes for when bedding alone cannot fix the problem.
When the room is too warm
Warmth is usually a combination of three things: the air temperature, trapped body heat, and still air. Heat is the disruption the evidence is clearest about, so address it in that order.
- Lower the thermostat a degree or two rather than several at once.
- Swap a heavy duvet for a lighter one, or use a breathable natural fill.
- Let air move — a fan pointed across the room, not directly at you, keeps the air from stagnating.
- Close curtains during the day in summer so the room starts the night cooler.
Watch the humidity, not just the heat
A warm and humid room feels far worse than a warm dry one. If the air feels clammy, deal with moisture first — see why the bedroom feels damp in the morning.
When the room is too cold
A cold room is usually better solved on the bed than in the air. You do not need to force a room down to 16°C to sleep well — warm the person, not the whole room:
- Add a duvet layer or a blanket that can be thrown off without waking you.
- Warm the bed itself with a hot-water bottle placed under the covers before you get in, then removed.
- Fix draughts at windows and doors before turning the heating up.
- Keep the room just cool — not cold. Cold rooms can also disrupt sleep, even if they are less harmful than hot ones.
Frequently asked questions
Is 16°C too cold to sleep in?
For many people, yes. It is the cold edge of older guidance and sits below what current recommendations and the more recent measured study suggest. Some people sleep well at 16°C, but it is not a target you need to hit.
Isn't 18°C too cold to be comfortable?
For plenty of people, yes — and that is normal. 18°C is the cool end of the sleep guidance, not a comfort target. Bedroom comfort also depends far more on your duvet and nightwear than on a one- or two-degree difference in the room, so a slightly cool room with a warm duvet often feels better than a warm room with a thin one. Go with the temperature that leaves you comfortable.
Is there one correct bedroom temperature?
No. 18–20°C is a sensible starting range, not a fixed rule. Your bedding, clothing, age and personal comfort all matter, so treat it as a point to adjust from.
Are cooler rooms always better?
No. Heat is more clearly disruptive to sleep, but a room that is too cold causes discomfort and can disturb sleep as well. Cool and comfortable beats simply cold.
Should I leave a window open all night?
Only if it keeps the room in a comfortable range without making it cold or letting in noise and pollen. A short airing before bed is often enough.
Does a fan actually cool the room?
A fan does not lower the air temperature, but it moves air across your skin, which helps you feel cooler and keeps the air from stagnating.
What about a baby's room?
Guidance for infants differs and usually suggests a slightly warmer room, plus careful attention to sleepwear and overheating. Follow the current advice from your health authority or midwife rather than a general bedroom guide.
Sources and research notes
This guide describes bedroom comfort, not medical treatment, and states comfort ranges rather than prescriptions. Guidance pages change, so each source is linked with the date we checked it.
Written and edited by the Resthearth Editorial. Each guide starts from a real bedroom decision, is checked against the sources listed above, and is updated when guidance changes. We are an independent editorial desk, not medical professionals — read how we research and update our guides.
