Baby Sleeping Bag TOG Guide: Which TOG for Which Temperature

Baby sleeping bags — also called sleep sacks or grobags — are widely recommended by safe sleep guidelines as a safer alternative to loose blankets in a baby's sleep space. But choosing the right one requires understanding the TOG system, which many parents find confusing at first.

What Is TOG?

TOG stands for Thermal Overall Grade, and it is a measure of a fabric's thermal resistance — in simple terms, how warm it is. The higher the TOG, the warmer the sleeping bag. The TOG system was originally developed for duvets and quilts, and it has been adopted by baby sleeping bag manufacturers to help parents choose appropriately for different room temperatures.

It is important to understand that TOG is a property of the sleeping bag itself, not of the total sleep system. You still need to dress your baby in appropriate layers underneath the sleeping bag, and the room temperature is the starting point for the whole calculation.

UK Room Temperature Context

The recommended temperature for a baby's sleep room in the UK, according to the Lullaby Trust and NHS guidance, is between 16 and 20 degrees Celsius. In practice, UK homes vary considerably by season, time of night, and whether the heating is on.

In summer, many UK bedrooms will exceed 20 degrees — sometimes significantly. In winter, rooms can drop to 16 degrees or below overnight, particularly in older or less insulated properties. You cannot rely on a fixed setting, which is why understanding the TOG system properly allows you to adjust.

A room thermometer in the baby's room is a worthwhile investment — you will use it every night and it removes the guesswork entirely.

Which TOG for Which Temperature

Here is a practical guide to matching sleeping bag TOG to room temperature:

24 degrees Celsius and above: 0.5 TOG. At very warm temperatures, even a 0.5 TOG bag may be too warm and some babies will sleep better in just a vest or light sleep suit without a bag at all.

21 to 23 degrees Celsius: 0.5 to 1 TOG. A light sleeping bag. Dress your baby in a short-sleeved vest or just a nappy underneath.

18 to 20 degrees Celsius: 1 to 2.5 TOG. This is the standard UK recommended sleep temperature, and a 2.5 TOG bag with a short-sleeved vest and a long-sleeved sleep suit is a common and appropriate combination.

16 to 17 degrees Celsius: 2.5 TOG. Add an extra layer underneath — a long-sleeved vest, a sleep suit, and possibly a light additional layer.

Below 16 degrees Celsius: 2.5 TOG with additional clothing layers. Some brands now offer 3.5 TOG bags for very cold rooms, though maintaining a minimum room temperature of around 16 degrees is preferable to layering more clothing.

Checking Temperature, Not Feeling Cold Hands

A common mistake is checking a baby's hands to assess whether they are warm enough. Babies' hands and feet are often cool even when their core temperature is perfectly normal — peripheral circulation in young babies is different from older children and adults. The reliable way to check your baby's temperature is to feel the back of their neck or their chest. These should feel warm but not hot or sweaty. If your baby is sweating, they are too warm — a risk factor for SIDS.

Overheating is a more significant safe sleep concern than being slightly cool. When in doubt, dress your baby slightly cooler rather than warmer.

Seasonal Guide for UK Homes

Summer (June to August): Most UK bedrooms will be 20 to 25 degrees at night without air conditioning. Have a 0.5 TOG bag ready and dress minimally underneath. Avoid long-sleeved sleep suits in warm weather.

Autumn (September to November): Room temperatures begin to vary more. A 1 to 2.5 TOG bag is usually appropriate, depending on whether the heating is on.

Winter (December to February): Central heating means many UK homes maintain temperatures of 18 to 20 degrees overnight if the heating is on a timer. A 2.5 TOG bag with appropriate layers is typically right. If the heating goes off overnight and the room cools significantly, consider a lower thermostat setting on a timer to keep the room within range.

Spring (March to May): Temperatures can swing considerably. Having both a 1 TOG and a 2.5 TOG bag accessible allows you to respond to changing nights without difficulty.

When to Move from a Sleeping Bag to a Duvet

NHS and Lullaby Trust guidance states that babies should not have a duvet until they are at least 12 months old. Before this, loose bedding in the sleep space is associated with increased SIDS risk.

In practice, many parents continue using sleeping bags well past 12 months — sometimes until 2 or 3 years old — because they are safer and more practical than duvets for children who move around in their sleep. There is no reason to rush the transition. When you do move to a duvet, choose one appropriate for the season and the room temperature, using the same principles as above.