TOG (Thermal Overall Grade) is a measure of the thermal insulation of textiles. The higher the TOG rating, the warmer the sleep sack. Common values are 0.5 TOG (summer), 1.0 TOG (spring/autumn), 2.5 TOG (all year) and 3.5 TOG (winter). The right value depends on the room temperature in the bedroom.

Sleep sack TOG calculator: which TOG at which room temperature?

Q: Which TOG at 18, 20 or 24 °C?

At around 18 °C a 2.5 TOG sleep sack fits, at 20 °C a 1.0 to 2.5 TOG sleep sack (transition) and from 24 °C a thin 0.5 TOG summer sleep sack. Rule of thumb: from 24 °C around 0.5 TOG, 20–24 °C around 1.0 TOG, 16–20 °C around 2.5 TOG and below 16 °C around 3.5 TOG.

Q: What should my baby wear in the sleep sack?

Under the sleep sack, depending on the room temperature, just a short-sleeve bodysuit (from 24 °C), a long-sleeve bodysuit or thin sleepsuit (20–24 °C) or bodysuit plus sleepsuit (below 20 °C). No hat and no loose blanket in bed. Check at the neck or chest whether it fits – warm and dry is right.

Q: From what age can I use a sleep sack?

A baby sleep sack can be used from birth as long as the size fits (neck opening tight enough that the head can't slip in, leg area wide enough). It replaces loose blankets, which are a safety risk in the crib. What matters is the right size and a TOG rating that matches the room temperature.

The TOG rating tells you how warm a baby sleep sack is – and the right value depends solely on the room temperature in the bedroom. Simply set the temperature below: the calculator immediately shows you the right TOG rating and what your baby should wear underneath.

In short: from 24 °C ≈ 0.5 TOG · 20–24 °C ≈ 1.0 TOG · 16–20 °C ≈ 2.5 TOG · below 16 °C ≈ 3.5 TOG. The ideal sleep temperature is 16–18 °C. When in doubt, slightly too cool rather than too warm.

What does TOG mean?

TOG stands for Thermal Overall Grade and is a measure of the thermal insulation of fabrics. The higher the TOG rating, the warmer the sleep sack keeps your baby. Because a sleep sack replaces loose blankets (which don't belong in the crib), the right TOG rating makes sure your baby neither gets cold nor overheats.

🌙

TOG calculator

Slide the room temperature – read off the right TOG rating & clothing underneath.

20°C in the bedroom

14°26°

Chart: TOG rating by room temperature

For everyone who prefers to look it up – the same recommendations as an overview:

Room temperature	TOG rating	Clothing underneath
from 24 °C	0.5 TOG (summer)	Just a short-sleeve bodysuit
20–24 °C	1.0 TOG (spring/autumn)	Long-sleeve bodysuit or thin sleepsuit
16–20 °C	2.5 TOG (all year)	Bodysuit + sleepsuit
below 16 °C	3.5 TOG (winter)	Bodysuit + sleepsuit, possibly thin socks

Safety & safe sleep

💤 The ideal room temperature is ~16–18 °C. Check at the neck or upper back whether your baby is at the right temperature – warm and dry is just right, sweaty means too warm. Hands and feet are often cooler and not a good indicator. No hat and no loose blankets or pillows during sleep – both increase the risk of overheating and sudden infant death syndrome (SIDS). TOG ratings are a guide; always follow the manufacturer's instructions for your sleep sack.

What should my baby wear in the sleep sack?

The principle: the warmer the room, the less underneath. From 24 °C a short-sleeve bodysuit is enough, between 20 and 24 °C a long-sleeve bodysuit or a thin sleepsuit, below 20 °C you combine bodysuit and sleepsuit. If it's cool below 16 °C, thin socks help as well. Make sure the sleep sack fits well: the neck opening must be tight enough that the head can't slip inside.

🧮 Open the full clothing calculator

Frequently asked questions

What does TOG mean?

TOG (Thermal Overall Grade) measures thermal insulation. The higher the value, the warmer the sleep sack: 0.5 TOG (summer), 1.0 TOG (transition), 2.5 TOG (all year), 3.5 TOG (winter).

Which TOG at 18, 20 or 24 °C?

At ~18 °C a 2.5 TOG sleep sack, at ~20 °C a 1.0–2.5 TOG sleep sack, from 24 °C a thin 0.5 TOG summer sleep sack.

What should my baby wear in the sleep sack?

From 24 °C just a short-sleeve bodysuit, 20–24 °C a long-sleeve bodysuit or thin sleepsuit, below 20 °C bodysuit + sleepsuit. No hat, no loose blanket.

From what age can I use a sleep sack?

From birth, as long as the size fits (tight neck opening so the head can't slip in). The sleep sack replaces loose blankets in the crib.

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 our own experience as parents – more in our story. Last updated: July 2026.

More dressing guides

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