Bedroom temperature: what the research actually supports

Search for the ideal bedroom temperature and you will find a confident answer: about 18°C, or somewhere between 60 and 67°F. It is repeated so often that it sounds like a research finding. We went looking for the study behind it and couldn’t find one.

What the research does show is more useful than a single number. It explains why temperature matters, which conditions clearly harm sleep, and which cheap tricks have real support.

Why your body wants to cool down

Falling asleep goes with a decline in core body temperature. To get there, your body opens up blood vessels in the hands and feet and sheds heat through the skin ¹. In a classic laboratory study, the warmth of people’s hands and feet relative to the rest of their body was a strong predictor of how quickly they fell asleep ².

This explains the apparent paradox at the centre of bedroom temperature advice. You want a room cool enough for heat to escape, but skin, especially at the extremities, that is warm enough to keep releasing it. A cold room that makes you clench up and keeps your feet freezing can work against you as much as a hot one.

Heat is the clearer problem

A review of the research found that the typical effects of thermal stress are more wakefulness and less deep sleep and REM sleep. In real life, where people use bedding and clothes, heat exposure is what reliably disrupts sleep stages ³. Cold, with adequate bedding, did not change sleep stages in the studies reviewed, although it did affect heart activity during sleep, so the authors cautioned that its impact may be underestimated.

Laboratory studies show how quickly heat bites:

• When 16 adults over 65 slept at 30°C rather than 27°C, they lost 26 minutes of total sleep and 5 minutes of REM sleep, spent 27 minutes longer awake, and their sleep efficiency fell by 5.5%, even with a ceiling fan running at 30°C ⁴.
• Humidity adds to the load. Young men sleeping in hot, humid conditions (35°C, 75% humidity) woke more and had less deep and REM sleep than in cooler or drier conditions ⁵.

Data from real homes agree. In a longitudinal study of older adults that used wearable sleep monitors and bedroom sensors, sleep was most efficient and restful when the night-time temperature was between 20 and 25°C. Sleep efficiency dropped by 5 to 10% as temperatures rose from 25 to 30°C, with large differences between individuals ⁶.

So what temperature should you aim for?

Here is what the studies actually measured:

The spread is the point. The “best” temperature depends on what you’re wearing, what is on the bed, how humid it is, how old you are and what you’re used to. A Beijing field study estimated a thermally neutral sleeping temperature of 26.5°C in naturally ventilated bedrooms during spring and autumn ⁷. That is well above the 18°C rule, and it reflects lighter bedding and a different climate, as well as reliance on a consumer wrist tracker.

If you want a starting point, the best real-home data we have suggest roughly 20–25°C (68–77°F), with the lower end better if you use heavy bedding ⁶. Then adjust bedding first and the thermostat second, because the temperature inside your bed matters more than the number on the wall.

Tricks that use your physiology

A warm bath or shower before bed

This sounds backwards for a body that wants to cool down, but it works by forcing the heat-dumping response. A meta-analysis pooled 13 studies of warm baths or showers before bed. Water at 40–42.5°C improved self-rated sleep quality and sleep efficiency, and when taken 1–2 hours before bed, even 10 minutes shortened the time it took to fall asleep ¹. The warm water draws blood to the skin of the hands and feet, which speeds heat loss afterwards.

The authors were careful to note that the research is limited, especially on the best timing and duration. We rate it moderate: consistent and plausible, but built on small studies.

Warm skin, deeper sleep

In an elegant laboratory study, researchers used a thermosuit to raise people’s skin temperature by just 0.4°C without changing their core temperature. It reduced night-time waking and shifted sleep towards deeper stages, especially in older adults, whose proportion of slow-wave sleep almost doubled and whose chance of waking too early in the morning fell sharply ⁸.

You can’t buy a laboratory thermosuit, but the principle supports keeping your skin comfortably warm under the covers while the room itself stays cool.

Bed socks

In a small randomised crossover study, six young men slept in a 23°C room with and without feet-warming bed socks. With the socks, they fell asleep 7.5 minutes faster, slept 32 minutes longer and woke less often, while their core temperature didn’t change ⁹. Six participants is far too few to generalise from, but it fits the physiology, costs almost nothing and has no real downside if your feet tend to be cold.

Humidity and ventilation

Temperature does not act alone. Humid heat is harder on sleep than dry heat ⁵, and in the study of older adults, better ventilation added about 10 minutes of deep sleep and nearly 4 minutes of REM sleep, with benefits that added to those of a cooler room ⁴. The Beijing field study also linked lower bedroom carbon dioxide, a marker of good ventilation, with better sleep quality ⁷. We will cover bedroom air quality in a dedicated article.

A practical checklist

1. Start around 20°C and adjust bedding before the thermostat. If you wake up hot, lighter bedding often helps more than a colder room.
2. Keep hands and feet warm if they run cold: bed socks are a cheap experiment.
3. Try a warm bath or shower 1–2 hours before bed, around 40–42°C, for at least 10 minutes.
4. Prioritise cooling in heatwaves. Heat is the condition most clearly linked to worse sleep. Block daytime sun, ventilate when it is cooler outside, and use lighter bedding.
5. Don’t chase a perfect number. There isn’t one. Notice how you sleep across a few weeks at different settings, and trust that more than a rule of thumb.

Temperature connects to the rest of your night: the drop in body temperature is part of the same daily rhythm that light and timing control. See our circadian rhythm guide for how the pieces fit together.