What Temperature Should Your Bedroom Be for Sleep?
5 min read
Quick answer: most sleep research lands somewhere around 18C as the bedroom temperature that suits the majority of people. That is a guideline, not a rule, and it is worth knowing why the number exists before you go to war with your thermostat. It also is not the number most Australian bedrooms actually hit, which is the more useful problem to solve.
Why there is a number at all
You do not fall asleep because you are tired. You fall asleep because your core body temperature drops.
That drop is the signal. In the hour or two before sleep, your body sheds heat through your hands, feet and face, core temperature falls by roughly a degree, and the fall is what lets you move from drowsy into actual sleep. It keeps falling overnight and bottoms out in the early hours of the morning.
A cooler room helps that happen. A warm room works against it. That is the whole reason a recommended bedroom temperature exists, and it is why every major sleep guideline says the same three words about a bedroom: dark, quiet, cool.
So is 18C right?
It is a reasonable middle. It is not a target you have failed to hit.
The figure comes from research on the average adult sleeping under normal bedding. Change the inputs and the right number moves. Someone sleeping alone under a light cover is not the same as two adults and a dog under a heavy one. Age shifts it. So does what you wore to bed, what you ate, what you drank, and where you are in your cycle.
There is also a practical problem with the number in Australia specifically. In a Sydney or Brisbane summer, 18C in a bedroom overnight is not something most people can reach without running air conditioning for eight hours, and plenty of homes do not have it at all.
So the honest version is this. Aim cooler rather than warmer. Do not treat 18C as a pass mark. And if you cannot move the room, move the layer that is touching you, because that is the one you can actually control.
The bit most people miss: the room is not what touches you
Here is the part that changes how you think about it.
Air is a poor conductor of heat. Fabric is a good one. The air in your bedroom is sitting a few centimetres away from your skin, doing very little. Your sheets are pressed directly against you for seven hours.
That means the temperature you experience overnight is much more about the fabric than the thermostat. You can cool a room to 18C and still overheat under a heavy, heat-trapping quilt cover. You can also sleep comfortably in a warmer room under a fabric that moves heat away from your skin as fast as your body produces it.
This is the reason a fan often disappoints. A fan moves air around a layer that is already holding your body heat. It does not fix the layer.
What actually cools a bedroom, ranked by how much it matters
1. The fabric against your skin. Biggest lever, cheapest to change, and the only one that works every night regardless of weather. More on how to judge this below.
2. Airflow through the room, not around it. One window open is a dead end. Two openings on opposite sides of the room gives you cross-ventilation and actually exchanges the air. If you only have one window, put a fan facing out of it rather than in, so it pushes hot air out and draws cooler air through the door.
3. Blocking heat before it arrives. A bedroom that has been baking behind a west-facing window all afternoon starts the night hot and stays hot. Closing blinds during the day does more than opening windows at night.
4. Your bed base and mattress. Memory foam holds heat. A slatted base breathes better than a solid one. This is expensive to change, which is why it is fourth.
5. The thermostat. It matters, but it is the most expensive lever and the one most likely to be unavailable at 3am when you are already awake.
How to tell if a fabric is actually cool
Almost every bedding brand in Australia uses the word breathable. It is not a measurement and nobody has to prove it.
There is a measurement, and it is called Qmax. It records how much heat moves from your skin into a fabric the instant the two touch, in watts per square centimetre. Higher means it pulls heat away faster, which is what "feels cool" actually is.
For a fabric to be described as cool to the touch at all, the accepted threshold is 0.18. That line is useful because most fabrics do not clear it.
| Fabric | Qmax (W/cmยฒ) |
|---|---|
| Evercoolยฎ+ (Rest sheets and pillowcases) | 0.445 |
| Evercoolยฎ (Rest comforter) | 0.433 |
| Cool-touch threshold | 0.18 |
| Silk | 0.19 |
| Bamboo viscose | 0.15 |
| Cotton | 0.11 |
Cotton sits at 0.11. It does not narrowly miss the cool-touch category. It does not qualify for it.
Our sheets and pillowcases test at 0.445, over four times cooler to the touch than cotton, tested by SGS to the JIS L 1927:2020 standard and published in full on our third-party test results page. If you want the method rather than the number, we have written a full explainer on Qmax.
The point is not the brand. The point is that a number exists, so you can ask any brand for theirs.
If you take one thing from this
Stop trying to win the room and start winning the 30 centimetres around your body.
A cooler bedroom genuinely helps, and if you can get yours toward 18C without a fight, do it. But for most Australians through most of the year that is not realistic, and the thermostat is not where the biggest gain is anyway. The fabric touching you for seven hours a night is.
Not sure which layer is causing your problem? Our 2 minute sleep quiz will point you at it. If you already know you run hot, start with the hot sleepers guide or go straight to the cooling sheets buying guide.
Frequently asked questions
What is the best bedroom temperature for sleep?
Most sleep research points to around 18C for the average adult, because your core body temperature needs to fall for you to get to sleep and stay there. It is a guideline rather than a rule. The right number shifts with your age, your bedding weight, whether you share the bed and what the climate is doing outside.
Is 18 degrees too cold to sleep in?
For most people it is not, because you are sleeping under bedding rather than in open air. If 18C feels too cold, the usual fix is a warmer layer on the bed rather than a warmer room, since the room temperature is what helps your body shed heat in the first place.
How do I cool my bedroom down without air conditioning?
Close blinds during the day so the room does not heat up in the first place, then create cross-ventilation at night with two openings on opposite sides rather than one window. A fan facing out of a window pushes hot air out. The biggest single change is usually the fabric on the bed, not the air in the room.
Does bedroom temperature matter more than bedding?
Bedding usually matters more, because air is a poor conductor of heat and fabric is a good one. The air in the room sits a few centimetres from your skin, while your sheets are pressed against it all night. A cool room under a heat-trapping quilt will still sleep hot.