The safest way to keep a newborn warm at night is with layered clothing and a wearable blanket, not loose bedding. The ideal nursery temperature is 16 to 20°C (roughly 61 to 68°F), which feels cooler than most adults expect. Getting this right matters because overheating is a known risk factor for sudden infant death, while the right layers and room temperature let your baby sleep both warm and safe.
The Right Room Temperature
Aim for 16 to 20°C (about 61 to 68°F) in your baby’s sleep space. That range feels slightly cool to most adults, which is exactly the point. Babies regulate body heat less efficiently than adults, and a room that feels comfortable to you in pajamas and a duvet can easily be too warm for a swaddled newborn.
A simple room thermometer placed near the crib gives you a reliable reading. Digital models that display the current temperature at a glance cost only a few dollars and take the guesswork out of nighttime adjustments. If your home runs cold in winter, a portable heater can help, but keep it on a solid, flat surface at least three feet from the crib, curtains, and anything else that could catch fire. Once the room reaches the target range, turn it off or use one with an automatic shut-off feature.
Clothing Layers and the One-Layer Rule
A good starting guideline: dress your baby in no more than one layer beyond what you’d wear to be comfortable in the same room. In a room at 68°F, that might mean a long-sleeved onesie under a lightweight sleep sack. In a cooler room closer to 61°F, a thicker sleep sack over a onesie with footed pajamas works well.
Footed pajamas, bodysuits, and onesies are the building blocks. You combine them based on how warm or cool the room is. Cotton and cotton-blend fabrics breathe well and reduce the chance of overheating. Avoid fleece or heavy knit fabrics unless the room is genuinely cold.
How TOG Ratings Work
TOG stands for Thermal Overall Grade, and it measures how much warmth a fabric traps. The higher the number, the warmer the garment. Most sleep sacks and wearable blankets list a TOG rating on the packaging, which makes choosing the right one straightforward once you know your room temperature.
- 0.2 TOG: Very lightweight, best for warm rooms between 75°F and 81°F (24–27°C).
- 1.0 TOG: Light to medium weight, suited for 68°F to 75°F (20–24°C).
- 2.5 TOG: Heavier weight for cooler rooms between 61°F and 68°F (16–20°C).
- 3.5 TOG: Extra warm, designed for rooms below 61°F (16°C).
When using a higher-TOG sleep sack, reduce the layers underneath. A 2.5 TOG sack over a long-sleeved onesie is plenty for most cool rooms. Pairing a thick sleep sack with heavy pajamas underneath is a common reason babies overheat at night.
Why Loose Blankets and Hats Stay Out of the Crib
Keep blankets, quilts, pillows, bumper pads, and soft toys out of your baby’s sleep area entirely. Loose bedding can cover a newborn’s face and create a suffocation risk. Wearable blankets and sleep sacks exist specifically to replace loose blankets, giving your baby warmth without the danger.
Indoor hats are another item to skip at bedtime. Babies release excess heat through their heads, and covering that surface makes it harder for them to cool down. A 2023 study found that hats placed on healthy full-term newborns at birth had no measurable benefit for temperature regulation, yet the practice can set a habit that leads to overheating later. Once your baby is home from the hospital, hats are for outdoor cold, not indoor sleep.
Signs Your Baby Is Too Warm
The quickest check is to touch the back of your baby’s neck or chest. If the skin feels hot or damp, they’re likely overdressed. Hands and feet that feel cool are normal for newborns because of immature circulation, so don’t use cold fingers as a reason to pile on layers.
Other signs of overheating include flushed or red skin, damp hair, unusual fussiness or restlessness, and rapid breathing. Some babies develop heat rash, which looks like tiny red bumps in skin folds, around the neck, or on the bottom. In more serious cases, a baby may become unusually sluggish, limp, or difficult to wake. If your baby’s skin feels clammy or their pulse seems unusually fast, remove a layer immediately and check that the room isn’t too warm.
Keeping the Temperature Steady All Night
Room temperature often drops in the early morning hours, which is why a consistent heating setup matters more than what the thermostat reads at bedtime. If you use central heating, setting it to maintain at least 61°F overnight prevents the room from dipping too low. If you rely on a space heater, choose one with a thermostat that cycles on and off to hold a set temperature rather than running continuously.
In summer or warmer climates, the challenge flips. A fan circulating air in the room can help, but point it toward a wall rather than directly at your baby. Dress your newborn in just a short-sleeved onesie or a diaper with a 0.2 TOG sleep sack when temperatures climb above 75°F. Keeping curtains closed during the day can prevent the nursery from absorbing heat that lingers into the evening.
A Practical Nighttime Routine
Before putting your baby down, check the room thermometer and pick your layers accordingly. A room at 66°F calls for a long-sleeved onesie under a 2.5 TOG sleep sack. A room at 72°F calls for a short-sleeved onesie under a 1.0 TOG sack. Lay your baby on their back on a firm, flat mattress with nothing else in the crib.
Do a quick neck or chest check about 20 minutes after your baby falls asleep, once their body has settled into the environment. If they feel warm and clammy, drop a layer. If they feel cool on the chest (not just the hands), consider a warmer sleep sack or an extra base layer. After a few nights of adjusting, you’ll find the combination that keeps your baby comfortable without constant monitoring.