Dressing your baby at night

At night, safe sleep comes first: a baby sleep sack instead of loose blankets, a rather cool room temperature and no overheating. How warm the sleep sack should be is told by its TOG rating – matched to the temperature in the bedroom.

In short: In the UK, keep the bedroom at 16–20 °C (NHS). In the US there is no set number: keep the room comfortable for a lightly dressed adult (AAP). Choose the sleep sack by TOG, underneath a bodysuit or sleepsuit – no hat, no loose blankets. Check for overheating at the chest or neck.

By Felix Plaschka, developer of HeyFini and dad of a daughter. Published 23 June 2026, last reviewed 23 June 2026.

We are parents, not doctors. This guide does not replace a visit to your midwife, health visitor or pediatrician. Facts and figures come from the sources listed. More about us.

TOG chart: sleep sack & what goes underneath

Room temperature	TOG rating	Under the sleep sack
from 24 °C	0.5 TOG · summer	Diaper only or a short-sleeve bodysuit
20–23 °C	1.0 TOG · spring and autumn	Short- or long-sleeve bodysuit
16–20 °C	2.5 TOG · all year	Long-sleeve bodysuit, plus a romper at ~16–18 °C
below 16 °C	3.5 TOG · winter	Long-sleeve bodysuit + warm sleepsuit

The sleep sack calculator shows you the right value directly for your room temperature.

Safe sleep

💤 Keep the bedroom on the cool side, in the UK at 16–20 °C (NHS). Babies are safer slightly too cool than too warm. No hat in bed, no loose blankets or pillows, a sleep sack in the right size, so your baby can't slip down inside it. Check for overheating at the chest or neck – not at hands or feet.

When it gets cooler at night

If the temperature drops below 18 °C you have two options: choose a warmer sleep sack (2.5 instead of 1.0 TOG) or put a long-sleeve bodysuit on under the 2.5 TOG sack. Both together only when it's really cold – and then check the neck in the morning.

🌙 Open the sleep sack calculator

Frequently asked questions

Which TOG rating at which temperature?

0.5 from 24 °C, 1.0 at 20–23 °C, 2.5 at 16–20 °C, 3.5 below 16 °C. In the UK, keep the bedroom at 16–20 °C (NHS). In the US there is no set number: keep the room comfortable for a lightly dressed adult and dress your baby in at most one layer more than you wear (AAP).

What goes under the sleep sack?

Depending on the temperature, from just a diaper or bodysuit to a long-sleeve bodysuit with a sleepsuit. The chart above shows the steps.

And without a sleep sack?

A sleep sack is safest. Otherwise a well-fitting sleepsuit, no loose blankets, no pillow, no hat.

By Felix & Merle · parents of Josefine

We built HeyFini out of our own everyday life with a baby. Our recommendations are based on recognised sources, among them the Lullaby Trust for safe sleep and the ADAC, Germany's automobile club, for car-seat safety, and on our own experience as parents – more in our story. Last updated: June 2026.

More dressing guides

General guidance, not medical advice. When in doubt, ask your paediatrician or midwife.

Never wonder again what your baby should wear

HeyFini suggests what fits based on the weather where you are, and predicts when the next feed and nap are due. Free on the App Store, no account needed.

Sources: Safe sleep and TOG values: The Lullaby Trust, the UK safer-sleep charity; room temperature in the UK: NHS; clothing layers and room temperature in the US: American Academy of Pediatrics (AAP) and NICHD Safe to Sleep; clothing in the car seat: ADAC, German automobile club, child seat guidance; overheating and the neck check: German Professional Association of Pediatricians (BVKJ).

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