Room thermometer or thermostat for baby sleeping bag tog?

Why isn’t the hallway thermostat the right number?

A thermostat tells the heating what to aim for in that zone. It does not tell you the air around the cot. Halls, landings and downstairs rooms often run cooler or warmer than a closed bedroom. The Lullaby Trust room-temperature page says it is hard to guess temperature, so use a room thermometer in the rooms where the baby sleeps.

A baby-monitor widget on a high shelf has the same problem if the camera sits above a radiator, in a draught, or several feet above the mattress. You are dressing the baby for the air they lie in, not the air at the ceiling or in the hall.

Where should the room thermometer sit?

Put it in the sleep room, at about cot-mattress height, and not on the radiator shelf or the window sill. Those surfaces run hotter or colder than the air the baby breathes. The Lullaby Trust also asks you to keep the cot or Moses basket away from a heat source or direct sun — a thermometer next to the radiator will copy that error.

1. 1
   Same room as the sleep space If the baby still rooms in with you, measure that bedroom, not the landing. The Lullaby Trust asks for room-sharing for at least the first six months.
2. 2
   Cot height, not a high shelf Fix or stand the thermometer so it sits near mattress height, a little away from the cot so it is not in the baby’s reach.
3. 3
   Away from radiators and windows A reading taken on a sunny sill or above a radiator is not the room. Move the sensor, then move the cot if it is against the heat source.
4. 4
   Read at bedtime, and again if the room changes South-facing rooms and top-floor flats often climb after a sunny day. Read again if you shut the door, turn the heating down, or wake for a night feed.
5. 5
   Open the bag’s own tog table The Lullaby Trust does not publish a universal clothing-and-tog chart. It asks you to follow the manufacturer’s tog guide for the room temperature you have just measured.

What number do I match to the sleeping bag tog?

Match the measured sleep-room temperature to the table printed on that bag’s hangtag, carton or care booklet. The NHS baby safer-sleep page lists typical commercial bands (2.5 tog for about 16–20°C, 1.0 tog for 20–24°C, 0.5 tog for 24–27°C). Those bands are a starting point only. The Lullaby Trust explains why it will not issue one chart: fabrics differ, trapped air between layers changes warmth, and every baby is different.

Official guidance treats 16–20°C as the usual comfortable range, with a lightweight, well-fitting sleep bag or light bedding. If you cannot hold that range, the Lullaby Trust still asks you to measure the room, use lighter or heavier clothing as the bag’s guide says, and check the baby’s chest or neck — not to guess from the outdoor forecast.

Should I leave the heating on all night instead?

The Lullaby Trust says it is rarely necessary to keep the heating on all night, and that an extra clothing layer usually helps if the room sits below the usual range. If you do leave heating on, it asks you to set it low, and no higher than 20°C. Which? (3 October 2025) reports the same NHS line: all-night heating is rarely needed; aim for 16–20°C regardless of the outdoor forecast.

A low thermostat in another room does not prove the cot-side air is 18°C. Measure the sleep room. If you use a portable heater to lift a cold room before bedtime, Which? records RoSPA-style advice to switch it off and take it out once the baby is down — and never to park the cot against a radiator.

• Hats stay off indoors. The Lullaby Trust says babies lose heat through the head; a hat in the cot can leave them too hot.
• No duvet, quilt or hot water bottle in the sleep space. NHS and Lullaby Trust both list these as overheating risks.
• If the bag is not warm enough, add a clothing layer or a higher tog — not a blanket on top of the bag.

Does a thermometer replace checking the baby?

No. The Lullaby Trust says every baby is different and the 16–20°C range is a guide. You still need to feel the chest or the back of the neck. Hands and feet are usually cooler; that is normal. If the skin on the chest or neck is hot or sweaty, remove a layer. If the chest feels cold, add a clothing layer or a higher tog from the bag’s table.

In shortDress from a cot-level thermometer in the sleep room, then the bag’s own tog table. A hallway thermostat or a high-shelf monitor widget is a different measurement. Official records still ask you to check the chest or neck; a number on the wall is not the whole job.