Room temperature

Keep the bedroom between about 18 and 25 °C (64–77 °F), and use bedding to fine-tune. Heat harms sleep more clearly than mild cool.

• Evidence: Some
• Low effort
• Low cost
• Works: tonight

Why it matters

Your core body temperature follows a daily rhythm and falls at night. Sleep is most likely to start while it is falling. Your body sheds that heat through the skin, especially the hands and feet, by sending more blood there [1].

A warm room makes that harder. A review of lab studies found that, with normal bedding and clothing, heat increases time awake and reduces deep sleep and REM sleep [1]. A 2024 systematic review of real-world studies found the same pattern: higher indoor or outdoor temperatures go with shorter, worse sleep, and the effect is stronger on the hottest nights [4].

Mild cool is less of a problem as long as you are covered. In one study the review describes, where people used bedding, sleep did not differ across room temperatures from 13 °C to 23 °C (55–73 °F) [1].

Room air vs the air in your bed

What your skin feels is the small pocket of air under the covers, not the room. When people sleep normally, that pocket stays around 32–34 °C (90–93 °F) [1]. Your duvet, sheets and sleepwear set that pocket. The room temperature matters because it changes how easily the bed can shed heat.

How to do it

1. Aim for 18–25 °C (64–77 °F). The low end is the World Health Organization’s minimum indoor temperature for health in cold seasons, a figure about health risks from cold homes rather than sleep [3]. The high end comes from a home study of older adults that used wearable sleep monitors and bedroom sensors: sleep was most efficient between 20 and 25 °C (68–77 °F), and sleep efficiency fell by 5–10% as the room went from 25 to 30 °C (77–86 °F) [2].
2. Get a cheap thermometer for the bedroom. Many people have no idea what their bedroom is at 3 a.m.
3. On hot nights, cool the room before bed. Close blinds during the day, open windows when it’s cooler outside, and use a fan or air conditioning if you have it.
4. Fine-tune with bedding, not the thermostat. If you wake up sweaty, use a lighter duvet. If you wake up cold, add a layer. See duvet weight and layering and bedding materials.
5. If you run hot or cold, move within the range. In the older-adult study, people differed a lot in which temperature suited them [2]. Two people in one bed can use separate duvets; see sharing a bed.

To plan your whole room, try the bedroom setup tool.

Common mistakes

• Treating 18 °C (65 °F) as proven. That number is everywhere, but we couldn’t find a sleep study that tested it as the best temperature. The 18 °C figure in WHO guidance is a minimum for protecting health in winter [3]. And WHO says the evidence can’t yet pin down the exact temperature below which harm starts [3].
• Making the room cold and sleeping uncovered. In lab studies of people with little or no bedding, cold disturbed sleep more than heat did [1].
• Ignoring stuffy air. In a lab study of 16 adults over 65, sleeping at 30 °C (86 °F) instead of 27 °C (81 °F) cut about 26 minutes of sleep. Better ventilation separately added deep and REM sleep [6].
• Assuming you’ll adapt to a hot room. The 2024 review found little evidence that people adjust quickly to heat [4].

Effect on your sleep score

• Efficiency and wake-ups: in a 14-day home study of 62 adults, sleep efficiency was 3.4% lower in the warmest fifth of bedroom temperatures than in the coolest fifth [5]. The older-adult study found a 5–10% drop from 25 to 30 °C [2].
• Total sleep, deep sleep and REM: all fall in heat in lab studies [1][6].
• HRV and heart rate: cold can change how your heart rate varies during sleep even when sleep stages don’t change [1]. In a lab study of 8 men sleeping at 3, 10 and 17 °C, the cold nights shifted HRV measures during light and deep sleep [7]. We found no study of how room temperature moves the HRV number on a consumer wearable.

How confident: fairly confident that heat lowers efficiency; less sure about exact amounts for healthy younger adults.

Evidence

Rated Some. A systematic review [4] and several observational and lab studies [2][5][6] agree that warm bedrooms worsen sleep. The best range is less certain. The 20–25 °C finding comes from older adults [2], and the lab studies are small, often with only young men or only older adults [1][7]. No trial has compared, say, 18 °C with 21 °C in healthy adults using their normal bedding.

General information for healthy adults, not medical advice. If you have a sleep problem that lasts, read when to see a doctor. Sources checked 4 October 2026. Spot a mistake? Tell us.