You have probably already read the number. Sixteen to eighteen degrees. Maybe you bought a little thermometer to check, put it on the bedside table, and discovered your bedroom sits at twenty one degrees in July whatever you do to it.
That is the point most people get stuck at. You have done the sensible things. Cotton bedding, a lighter duvet, window open, curtains shut all afternoon. And it still does not make much difference.
So before we repeat the number, it is worth being clear about what it is. It is a range that shows up consistently in sleep guidance and a reasonable thing to aim at. It is not a target most British bedrooms can hit, and treating it as a pass or fail test is a good way to spend money on the wrong things. Our sleep environment range is for the part of this you can genuinely control, which is a smaller part than the advice usually admits.
What the recommended range actually is
The Sleep Charity puts the ideal bedroom temperature at around 16 to 18°C. More usefully, it gives the edges as well as the middle: temperatures over 24°C are likely to cause restlessness, and a cold room of around 12°C makes it difficult to drop off at all.
The edges matter more than the midpoint. The gap between 18°C and 21°C is not where most people's sleep problems live. The gap between 21°C and 26°C, which is where a south facing British bedroom sits during a warm spell, very much is.
What the research supports, and how firmly
The direction of the evidence is clear. The precision is not.
A systematic review by Chevance and colleagues, published in Sleep Medicine Reviews in 2024, pulled together 27 studies on ambient heat and sleep across a range of countries and ages. Its conclusion: higher outdoor or indoor temperatures are negatively associated with both sleep quality and sleep duration. The effect was strongest in warmer months, in warmer climates, and among older and lower income groups.
That is a real finding, and it is worth knowing the limits of it. The authors were direct about the weaknesses in the field they were reviewing: only around 41% of the studies adjusted for seasonality, few looked at the delayed effects of heat over several days, most measured outdoor temperature rather than the temperature of the room people were actually sleeping in, and 42% of the studies were American. So "heat disrupts sleep" is well supported by the review. "Your bedroom must be 17.2°C" is not something this literature can tell you.
Why British bedrooms fight the number
This is the part that most articles on this topic skip, and it is the reason the advice feels useless when you are lying awake.
British housing was built to hold heat in, not to let it out. The English Housing Survey for 2024 to 2025 found that around 3 million homes in England, roughly 12% of occupied dwellings, reported getting uncomfortably hot. Of those households, 90% dealt with it by opening a window and 59% by switching on a fan. Only 7% used air conditioning.
So when guidance tells you to keep the room at 16 to 18°C in summer, it describes something almost nobody here has the equipment to do. You are not failing at sleep hygiene. You are being asked to control a variable you have no lever for.
It is getting harder, not easier. The Met Office defines a tropical night as one where the temperature never drops below 20°C, and found that three consecutive tropical nights in July has gone from a less than 1% chance in a pre-industrial climate to roughly 20% per year today. On those nights the outdoor air is above the recommended range before you have closed the front door.
The winter conflict nobody mentions
This tension is worth naming plainly, because it catches people out.
The sleep range is 16 to 18°C. UK public health guidance goes the other way. GOV.UK's cold weather advice says to heat the rooms you spend a lot of time in, including the bedroom, to at least 18°C, and lists who that matters most for: people over 65, people with cardiovascular, respiratory or mental health conditions, pregnant women, children under five, and people with limited mobility.
The two are not really in conflict, but the framing makes them look it. The sleep range is about comfort for a healthy adult. The 18°C floor is about health risk in the cold. If you fall into one of those groups, or live with someone who does, the health floor wins. Do not chill a bedroom to 16°C for the sake of a number you read in a sleep article.
For everyone else, the practical middle ground is what the Energy Saving Trust recommends anyway: set the thermostat to the lowest comfortable temperature, for most people between 18°C and 21°C, and use thermostatic radiator valves to run individual rooms lower than the rest of the house. A bedroom is the obvious candidate. The Trust puts the saving from dropping the thermostat one degree, from 22°C to 21°C, at around £120 a year in Great Britain and £80 in Northern Ireland.
Control the bed and the body, not just the room
If the room is largely out of your hands, the useful question changes. Not "how do I get this room to 17 degrees", but "how do I lose heat, or hold it, at the surface I am actually touching".
In summer, that means reducing what traps heat against you rather than trying to cool a whole room. Fewer layers, a lower tog duvet or a sheet, and bedding that moves moisture away rather than holding it. A cooling summer quilt or a cooling ice silk pillowcase works on a material basis: smoother, less absorbent fibres feel cooler against skin and hold less moisture than brushed cotton. That is a comfort effect, not a medical one, and it will not turn a 26°C room into an 18°C one. It can be the difference between damp and settled at the point of contact, which is often what people mean when they say they are too hot. On silk specifically: the friction and moisture properties are real and modest. The skin and anti-ageing claims attached to it are marketing rather than independent evidence.
In winter, the opposite logic applies. A cooler room with warmer bedding is easier to sleep in than a hot room with thin bedding, and it is cheaper. Layers you can shed at two in the morning beat one heavy solution. If you use a weighted blanket, use it for the weight and the feel of it rather than as a warmth strategy, because they do run hot, and plenty of people who buy one in November quietly stop using it in June. Our cotton weighted blanket is the more breathable option if that is a concern.
When it is not a temperature problem
Temperature is a common cause of broken sleep. It is not the only one, and it is worth knowing when you are working on the wrong thing.
If you wake up hot and drenched most nights regardless of the season, the room may not be the driver at all. Night sweats that keep happening, especially alongside weight loss, fevers, or a change you cannot explain, are worth raising with your GP rather than solving with a new duvet.
If you wake repeatedly at the same time each night and the room is a comfortable temperature, that is a different pattern with different causes. Our piece on why you cannot stay asleep covers that ground.
And if you have been sleeping badly three or more nights a week for three months or longer, that is the point at which it stops being a run of bad nights and becomes something worth taking to your GP. What the NHS recommends first for persistent insomnia is CBT-I, a structured talking programme, not a product. No amount of adjusting your bedding will substitute for it.
If a fixed wind-down is the piece you are missing rather than the temperature, start with our guide to building a pre-sleep routine instead.
The short version
Aim for 16 to 18°C if you can reach it. Treat above 24°C as the line where sleep reliably suffers, and 18°C as a floor rather than a ceiling if anyone in the house is in a vulnerable group. Then stop optimising the room and start optimising the bed, because that is the part you can change.
Driftward was built around this sort of question, and answers that are honest about their own limits. More on why, on our story page.