Quick Answer
Dressing a baby appropriately for sleep is one of the most practical and most anxiety-inducing parts of early parenthood, partly because the stakes feel high (overheating is a recognised risk factor for SIDS) and partly because the guidance is often presented as more complicated than it needs to be. The core principle is straightforward: keep the sleep environment between 16 and 20 degrees Celsius (61 to 68 degrees Fahrenheit), dress the baby in one more layer than an adult would find comfortable in the same room, use a tog-rated sleeping bag instead of loose blankets from birth, and check temperature by feeling the back of the neck or the chest rather than the hands or feet. This article covers the room temperature guidance, how to use the one-layer rule, how sleeping bag tog ratings work, how to adjust for seasonal changes, and the signs that a baby is too hot or too cold.
The Right Room Temperature for Baby Sleep
The room temperature most consistently associated with safe infant sleep is between 16 and 20 degrees Celsius (61 to 68 degrees Fahrenheit). This range is supported by The Lullaby Trust (the leading UK SIDS charity) and is consistent with AAP safe sleep guidance. The ideal within this range for most babies is around 18 degrees Celsius (64 degrees Fahrenheit).
This range feels cool to many parents, particularly those who are accustomed to sleeping in warmer rooms or who are worried about the baby being cold. The reasoning is that the risk of overheating in infant sleep is well established as a SIDS risk factor, while the risk of a baby being slightly too cool is generally less acute, provided the baby is appropriately dressed. A room that feels slightly cool to an adult is appropriate for a baby in a well-fitted sleeping bag.
A room thermometer placed at the level of the cot (not mounted high on the wall, where temperatures are higher) gives the most accurate reading of the temperature the baby is actually sleeping in. Many baby monitors now include room temperature readings, which is a useful feature for overnight monitoring.
The One-Layer Rule
The most practical guide for dressing a baby for sleep is to add one more layer than an adult would find comfortable in the same room at the same temperature. If you would sleep comfortably in a light long-sleeved top, the baby needs that plus one additional layer, which is typically provided by the sleeping bag.
In practice, at the recommended room temperature of around 18 degrees Celsius, most babies sleep comfortably in:
- A short-sleeved bodysuit (onesie) under a 2.5 tog sleeping bag for a standard cool room
- A long-sleeved bodysuit under a 2.5 tog sleeping bag for a room at the cooler end of the range
- A short-sleeved bodysuit under a 1.0 tog sleeping bag for a warm room in summer
The sleeping bag replaces the blanket and is the primary variable adjusted for temperature rather than adding or removing clothing layers, which is harder to do during the night without fully waking the baby.
How to Check if Your Baby Is the Right Temperature
The hands and feet of a baby are unreliable temperature guides: they are naturally cooler than the core body temperature and will feel cool even in a comfortably warm baby. The correct place to check temperature is the back of the neck, the chest, or the tummy, which reflect the baby's core temperature accurately.
- Too hot: Skin feels hot and sweaty, particularly at the back of the neck. The baby may appear flushed, be breathing more rapidly than normal, or seem restless and unsettled despite being otherwise well
- Too cold: Skin feels cold to the touch at the chest or back of the neck. The baby may be unsettled or wake frequently. Note that cool hands and feet alone are not a sign of being too cold
- Just right: Skin feels warm but not hot or sweaty at the chest or back of the neck. Hands and feet may be cooler than the torso; this is normal
Sleeping Bag Tog Ratings Explained
Sleeping bags for babies are rated by tog, the same thermal resistance measurement used for adult duvets. Higher tog means more warmth. Most baby sleeping bag manufacturers offer bags in three or four tog ratings, and choosing the right one for the room temperature is more important than layering clothing underneath.
General tog guidance by room temperature:
- Below 16°C (61°F): 3.5 tog sleeping bag with a long-sleeved bodysuit and potentially a light additional layer underneath
- 16 to 20°C (61 to 68°F): 2.5 tog sleeping bag with a short or long-sleeved bodysuit depending on the specific temperature
- 20 to 24°C (68 to 75°F): 1.0 tog sleeping bag with a short-sleeved bodysuit or just a nappy in very warm conditions
- Above 24°C (75°F): 0.5 tog sleeping bag or a light swaddle blanket (for newborns) with just a nappy, or no sleeping bag if the room is very warm. In very high temperatures, ensuring good ventilation and air circulation in the room is a priority
The fit of the sleeping bag matters as much as the tog rating. A bag that is too large allows the baby to slip down inside it, which is a safety hazard. Sleeping bags should fit snugly at the shoulders with no excess room at the neck opening, and should be the correct size for the baby's length.
Swaddling in the Newborn Period
For newborns, swaddling is a common and evidence-supported sleep practice that mimics the containment of the womb, reduces the startle reflex that frequently wakes young babies, and promotes longer sleep stretches in the early weeks. Safe swaddling practices are important:
- Swaddle with the hips loose: the legs should be able to bend up and out at the hips (the frog position). Tight swaddling of the hips and legs is associated with developmental hip dysplasia
- The swaddle should be secure at the chest but not so tight that it restricts breathing or chest expansion
- Stop swaddling as soon as the baby shows signs of rolling, which is typically from around 3 to 4 months. A swaddled baby who rolls onto their front cannot use their arms to push up, which is a serious safety risk
- The swaddle replaces other layers: account for the thermal contribution of the swaddle when choosing the tog of any additional sleeping bag used in combination with it
Seasonal Adjustments
Room temperature varies with season, and the baby's sleep setup needs to adjust with it:
- Winter: Central heating keeps many homes warmer than expected overnight. Check the actual room temperature rather than assuming it is cold because it is winter. A room heated to 22 degrees overnight requires a lower tog sleeping bag than the season might suggest
- Summer: Rooms that are comfortable during the day can become significantly warmer overnight, particularly in upper floors or rooms that receive afternoon sun. Use a low-tog sleeping bag or just a light blanket swaddle for newborns, ensure good ventilation, and consider a fan to circulate air (not directed at the baby, but circulating room air). Do not use a room air conditioner set to a temperature below 16 degrees
- Seasonal transitions: Autumn and spring often produce the greatest variability in overnight room temperature, with rooms cooling significantly between early evening and the early morning hours. A middle-tog sleeping bag (2.5) with adjustable clothing underneath (bodysuit only or bodysuit plus light layer) gives the most flexibility for this variability
What to Avoid
- Loose blankets in the cot for babies under 12 months. Loose bedding is a suffocation and overheating risk. A well-fitted sleeping bag eliminates the need for blankets and is safer in all temperature conditions
- Hats indoors. Babies lose a significant proportion of body heat through their heads, which is why outdoor hats are important in cold weather. Indoors during sleep, a hat prevents this natural heat regulation and contributes to overheating. Hats should not be worn during sleep indoors
- Electric blankets, heated mattress pads, or hot water bottles in or near the cot. These cannot be regulated reliably and create an overheating risk
- Overdressing relative to room temperature. More layers are not safer: overheating is the risk to avoid. When in doubt, err toward slightly less rather than more
- Sleeping bags that are too large. Sizing down if in doubt is the safer choice: a snug fit prevents the baby from slipping inside the bag
Key Takeaway
Keep the sleep room between 16 and 20 degrees Celsius (61 to 68 degrees Fahrenheit) and use a room thermometer at cot level for an accurate reading. Dress the baby in one more layer than an adult would find comfortable in the same room, using the sleeping bag tog as the primary variable rather than adding clothing layers. Check temperature at the back of the neck or chest, not the hands or feet. Choose sleeping bag tog by room temperature: 2.5 tog for the standard recommended range, adjusting up or down for cooler or warmer rooms. Swaddle newborns with hips loose and stop swaddling at the first signs of rolling. Avoid loose blankets, indoor hats during sleep, heated mattress pads, and sleeping bags that are too large.
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This article is for informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always follow current safe sleep guidelines from your national pediatric authority and consult your pediatrician with any concerns about your baby's sleep environment.