Key highlights
- Aim for 16–20°C (61–68°F) in the room your baby actually sleeps in.
- Use a reliable room thermometer — not the household thermostat.
- Check the temperature at bedtime, not in the afternoon.
- In heatwaves, cool the room before you reduce clothing.
- In winter, layer underneath the sleep sack rather than turning the heating up.
The widely cited safe range for a baby's nursery is 16°C to 20°C (61–68°F). This range is recommended by The Lullaby Trust and the NHS in the UK, echoed by NCT, and closely matched by Red Nose Australia, which suggests a room that feels comfortable for a lightly dressed adult. Below 16°C, the room may be too cold for a young baby; above 20°C, the risk of overheating increases.
Why the room matters more than the outfit
Sleepwear and TOG ratings only work if you know what temperature you're dressing for. Two babies in the same 2.5 TOG sleep sack — one in a 17°C room, one in a 24°C room — are in completely different thermal situations. Getting the room right first makes every other decision easier.
Rooms upstairs, rooms in the roof, and rooms with west-facing windows can easily run 3–5°C warmer than the ground floor at bedtime. A digital thermometer next to the cot — not the hallway thermostat — is the only way to know what your baby is actually sleeping in.
In hot weather and heatwaves
When outdoor temperatures climb, The Lullaby Trust recommends cooling the room before reducing clothing. Close blinds and curtains during the day to keep sunlight out, open windows in the evening once the outside air is cooler, and use a fan aimed awayfrom the cot to circulate air. Moving your baby to the coolest room in the house for the night is safer than leaving them in a room above 25°C.
If the room stays above 24°C, drop to a 0.5 or 1.0 TOG sack with a single light layer underneath. Above 27°C, a nappy and light vest only — with no sleep sack — is the guidance from most sleep sack manufacturers and safer sleep organisations.
In winter and cold rooms
If your nursery struggles to reach 16°C overnight, add layers underneath a 2.5 TOG sleep sack — a long-sleeved vest plus a sleepsuit works for most babies down to the low-teens. Avoid heaters, hot water bottles or electric blankets in or on the cot, and never cover your baby's head or face. A thermostatically controlled heater set on low, well away from the cot, is safer than adding blankets on top.
Quick rule of thumb
If the room feels comfortable to you in a light T-shirt, it's probably in the safe range for your baby. If you're reaching for a jumper, add a layer underneath the sleep sack — not on top.
Once you know the temperature of the room your baby actually sleeps in, choosing the right TOG and layers becomes a routine — not a nightly guessing game.