The best temperature for sleep, for most adults, is a bedroom somewhere around 16–18°C. That is cooler than many UK living rooms in the evening, and cooler than a bedroom with the radiator running until midnight. It is not a rule, and comfort varies a great deal from person to person, but it is the range that sleep researchers and organisations such as The Sleep Charity most often point to.
The reason is simple: your body needs to lose a little heat to fall asleep. A cool room makes that easier. A warm room fights it.
The rest of this guide explains the mechanism in plain terms, why the "right" number moves with the seasons and with the person, and how to get a UK bedroom into a good range without either freezing in January or lying awake sweating in July.
Why a cool room helps you sleep
Your core body temperature is not constant. It rises through the day, peaks in the late afternoon and early evening, and then starts to fall as bedtime approaches. That drop, of around half a degree to one degree, is one of the strongest signals to your body clock that it is time to sleep.
To shed that heat, your body sends warm blood to the skin, particularly the hands and feet. Warm hands and feet at bedtime are a sign this is working. A cool room lets the heat escape; a hot room traps it, so the drop stalls and sleep is slower to arrive and lighter once it does.
This is why a warm bath or shower before bed can help: the warm water pulls blood to the skin, and once you step out you lose heat quickly. It is also why a warm room so often causes waking in the early hours, when sleep is lighter and more easily disturbed by heat.
In short: Sleep arrives more easily when your body can lose a little heat. Aim for a cool room and a warm bed, not a warm room.
Why 16–18°C, and why it is only a guide
The 16–18°C range comes from a mix of laboratory studies and practical advice. Research reviewed by Harding, Franks and Wisden in Frontiers in Neuroscience (2019) found that sleep is most stable when the microclimate under the covers sits in a comfortable, slightly warm band, while the room itself stays cooler. In other words, the temperature that matters most is the one against your skin, and a cool room simply makes that easier to manage.
Several things shift the ideal number for you:
- Bedding. A 13.5 tog duvet in an 18°C room can feel like a 10.5 tog duvet in a 15°C room. The duvet, not the thermostat, does most of the work.
- Age. Older adults often feel the cold more and tend to prefer a warmer room. Babies and small children have their own guidance.
- Health and hormones. Menopause, some medications, thyroid problems and fevers all change how warm you run at night. If night sweats are new or persistent, that is worth raising with a GP.
- Partners. Two people in one bed rarely have the same ideal temperature. Separate duvets solve more arguments than a thermostat ever will.
If you wake sweaty or kick the covers off, your room is probably too warm for you. If you wake with cold shoulders and cannot settle, it is too cold. Adjust from there rather than chasing a number.
The UK problem: heating on too late
Most UK homes are heated by radiators on a timer, and it is common for the heating to run until 10pm or later. A bedroom that has been warming all evening can easily be at 20–22°C when you get in, with the radiator still ticking.
Two small changes make a big difference:
- Set the heating to switch off an hour or so before bed. The room will drift down towards a comfortable range while you are winding down. If you have a smart thermostat or radiator valves, set the bedroom lower than the living room in the evening.
- Turn the bedroom radiator valve down. Many bedrooms do not need heating in the evening at all if the rest of the house is warm. A thermostatic valve set to 2 or 3 rather than 5 is often enough.
If the heating comes on early in the morning, be aware that a room warming rapidly at 6am can wake you before your alarm. Setting the morning heating to start a little later, or lower, can help if you find yourself waking too early.
Winter: cool room, warm bed
The principle for cold months is "cool room, warm bed". A bedroom at 16°C feels fine under a 13.5 tog duvet with a decent mattress underneath you, and many people sleep better this way than in a heated room. Cold air on your face and warm covers over your body is close to ideal.
Where it goes wrong is a cold room and a thin duvet, or a cold room with a draught across the bed. If you are genuinely too cold to sleep, warm the bed rather than the room: a hot water bottle placed in the bed twenty minutes before you get in, bed socks, or a warmer duvet all work well. There is a fuller guide to sleeping well when it is cold.
Keep in mind that a very cold bedroom, below about 12°C, is not just uncomfortable. For older people and anyone with heart or lung conditions, NHS winter guidance is to keep living rooms and bedrooms warm enough, so do not treat the 16°C figure as a target to push below.
Summer: the hard part in a UK home
Without air conditioning, keeping a bedroom at 18°C in a July heatwave is not realistic. A top-floor flat with a south-facing window can sit at 26°C or more at midnight. The aim in summer is not to hit the ideal range but to get as close to it as you can and to help your body lose heat in other ways.
The basics are keeping the sun out during the day (blinds and curtains closed on the sunny side), opening windows in the evening once the outside air is cooler than the inside, and using a fan to move air across your skin. A lightweight summer duvet of around 4.5 tog, or just a sheet, replaces the winter bedding. A lukewarm shower before bed helps more than a cold one, because cold water can make your body hold on to heat.
There is a dedicated guide to sleeping when it is hot in a home without air conditioning, which goes through all of this in detail.
Getting the bedding right
Because the temperature under the covers matters more than the temperature of the room, bedding is your main tool. UK duvets are rated in tog, a measure of how well they insulate. The common ranges are roughly 4.5 tog for summer, 10.5 tog for spring and autumn, and 13.5 tog for winter. An all-seasons duvet is usually two duvets that clip together, giving you three options.
Fabric matters too. Cotton and linen breathe and wick moisture; polyester bedding tends to trap heat, which is why a polyester sheet in a warm room can feel clammy. For people who run hot, a cool-feeling pillow can also make a surprising difference, because the head loses a lot of heat. Our bedding and duvet tog guide covers the fabrics and fills in more depth.
If you tend to run warm at night
These are the two changes hot sleepers most often find worthwhile: a cooler pillow and a lighter duvet.
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Gel-layer cooling pillow
Example: Various (gel-topped memory foam)
Cooling pillows commonly combine memory foam with a gel layer or gel-infused foam, and are marketed as feeling cooler to the touch. The cooling effect is usually most noticeable at first contact rather than all night.
- Best for
- Hot sleepers who like foam support
- Key feature
- Gel-infused or gel-layered foam marketed to draw heat away from the head
- Why it may help
- If you wake up hot, the pillow is one of the warmest contact points. A breathable or gel-layered pillow paired with a cool room can help.
- Worth knowing
- Cooling claims vary and are hard to compare; a breathable cover and cool room matter as much as the pillow itself.
Lightweight summer duvet (around 4.5 tog)
Example: Various UK brands
Tog is the UK measure of a duvet's warmth. Duvets around 4.5 tog are marketed as summer weight; all-season sets combine a summer and a mid-weight duvet that clip together for winter.
- Best for
- Hot sleepers and UK summers
- Key feature
- Low tog rating for minimal insulation
- Why it may help
- Swapping a 13.5 tog winter duvet for a summer weight one is one of the simplest ways to stop waking up hot.
- Worth knowing
- Fill (down, feather, microfibre, wool) affects breathability as much as tog.
A simple way to check your room
A cheap room thermometer on the bedside table, read when you go to bed and again if you wake in the night, will tell you within a week whether your bedroom is running warm. Many people are surprised to find it is 21°C or more at 11pm. If it is, try one change at a time and give each a few nights before judging.
The short version
Set the heating to go off before bed, keep the bedroom cooler than the rest of the house, and put the warmth in the bed rather than the air. If you run hot, switch to a lighter duvet and breathable cotton before you buy anything else.
Temperature is one part of the picture. The other big ones are darkness and quiet, and the Sleep Environment guides cover each of them in turn. If you wake hot in the night regardless of the season, the guide to waking up hot at night looks at the other causes worth ruling out.
Frequently asked questions
Is 20°C too warm for sleeping?
For many adults, a bedroom held at 20°C overnight feels slightly warm, especially under a 10.5 or 13.5 tog duvet. It is not harmful, but if you wake sweaty or throw the covers off, try turning the heating off earlier or switching to a lighter duvet before you change anything else.
What temperature should a bedroom be for a baby?
UK guidance for babies is a little different from the adult range: the Lullaby Trust and the NHS suggest keeping the room at around 16–20°C, with a baby sleeping on their back in a clear cot. Follow their advice rather than adult bedroom guidance, and speak to your health visitor with any questions.
Sources and further reading
- NHS: Sleep and tiredness
- Frontiers in Neuroscience: Harding EC, Franks NP, Wisden W. The Temperature Dependence of Sleep. Frontiers in Neuroscience, 2019
- The Sleep Charity: The Sleep Charity
- Sleep Foundation: Sleep Foundation
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Written and reviewed by the Quiet Mind Sleep editorial team in line with our editorial policy. Spotted an error? Let us know.
