By Angelica Videla — Certified Baby and Toddler Sleep Consultant, London | Supporting families across the UK, Europe, US, and Australia
Quick Answer
TOG measures how warm a sleeping bag keeps your baby. For a room at 16 to 20°C, use 2.5 TOG. For 20 to 24°C, use 1.0 TOG. Above 24°C, use 0.5 TOG or a muslin sleeping bag. Always check room temperature rather than the season — UK homes vary enormously. The most common mistake is using too high a TOG, which causes overheating and more frequent night waking.
What does TOG mean?
TOG stands for Thermal Overall Grade. It measures the thermal resistance of a fabric — essentially, how effectively it retains heat. A higher TOG means more warmth. A lower TOG means less warmth and more breathability.
In practical terms: a 2.5 TOG sleeping bag keeps your baby significantly warmer than a 1.0 TOG. Using the wrong TOG for your room temperature is one of the most common and easily fixable causes of disrupted baby sleep.
TOG guide by room temperature
Below 16°C: 3.5 TOG (rare — only needed in consistently cold homes). Dress in a long-sleeve bodysuit and pyjamas underneath.
16 to 18°C: 2.5 TOG with a long-sleeve bodysuit underneath.
18 to 20°C: 2.5 TOG with a short-sleeve bodysuit underneath. This is the most common UK combination.
20 to 22°C: 1.0 TOG with a long-sleeve bodysuit underneath.
22 to 24°C: 1.0 TOG with a short-sleeve bodysuit underneath.
24 to 26°C: 0.5 TOG with a short-sleeve bodysuit or just a nappy.
Above 26°C: 0.5 TOG with just a nappy, or a muslin sleeping bag. Consider whether a sleeping bag is needed at all.
Why UK families need to measure room temperature
UK homes vary enormously in temperature. A Victorian terrace in January might have a bedroom at 15°C. A modern flat with underfloor heating might sit at 22°C year-round. Central heating that kicks in at 6am can push a room from 17°C to 21°C in the final hours of sleep — exactly when early morning waking is most likely.
A reliable nursery thermometer is essential. See our guide: best nursery thermometers for baby sleep.
How to check if your baby is the right temperature
Check the back of the neck or chest. This is the most reliable indicator. The skin should feel warm and dry — not hot, sweaty, or cold.
Ignore the hands and feet. Babies naturally have cooler extremities. Cold hands do not mean your baby is cold.
Signs of overheating: Sweaty back or neck, damp hair, flushed cheeks, restless sleep, frequent waking.
Signs of being too cold: Cool chest or tummy, mottled skin, unusually early waking.
Seasonal TOG guide for the UK
Winter (November to March)
Most UK homes need a 2.5 TOG sleeping bag in winter. If your home is well insulated and consistently above 20°C, 1.0 TOG may be sufficient. Measure your nursery temperature at bedtime and again at 3am to understand the overnight range.
Spring and Autumn (April, May, September, October)
These are the most challenging seasons because room temperature can vary by 5 to 8 degrees between one week and the next. Having both a 1.0 TOG and 2.5 TOG available allows you to switch based on the actual room temperature rather than the calendar.
Summer (June to August)
In a heatwave, room temperatures above 24°C are common in UK homes. Use 0.5 TOG or a muslin sleeping bag. In rooms above 27°C, your baby may sleep in just a nappy with no sleeping bag.
Early morning waking increases significantly in summer due to both light and heat. See our guide on blackout blinds for baby sleep.
Common TOG mistakes
- Using the same TOG year-round — room temperature changes and your sleeping bag should change with it
- Adding blankets on top of a sleeping bag — this is unsafe under 12 months and causes overheating at any age
- Going by the season rather than actual room temperature
- Using fleece sleepsuits inside a sleeping bag — fleece traps heat and can cause overheating even in a 1.0 TOG bag
- Assuming your baby is cold because their hands are cool
How temperature affects baby sleep
Research consistently shows that a room temperature of 16 to 20°C is optimal for baby sleep. Above 20°C, sleep becomes lighter and more fragmented. Below 16°C, cold discomfort can cause early waking.
Getting the TOG right is one of the simplest and most impactful changes a family can make. I recommend it as a first step for almost every family I work with before addressing more complex schedule or settling issues.
If temperature is sorted and your baby is still waking frequently, the issue is likely schedule or association-related. See our night wakings guide.
Frequently Asked Questions
What TOG should a baby sleeping bag be in winter?
2.5 TOG for rooms at 16 to 20°C, which covers most UK homes in winter. If your home is warmer than 20°C, use 1.0 TOG instead.
What TOG for summer?
0.5 TOG for rooms above 24°C. 1.0 TOG for rooms between 20 and 24°C. On very hot nights above 27°C, a nappy alone may be sufficient.
Can my baby overheat in a 2.5 TOG sleeping bag?
Yes — if the room is above 20°C or if your baby is wearing too many layers underneath. Always check the back of the neck for warmth and sweat.
How many TOG sleeping bags do I need?
Ideally two: a 2.5 TOG for cooler months and a 1.0 TOG for warmer months. A 0.5 TOG is useful during heatwaves.
Do I need a 3.5 TOG sleeping bag?
Only if your baby’s room consistently falls below 16°C. This is rare in most UK homes with central heating.