The simplest starting rule: dress your baby in one more layer than you’d wear yourself in the same conditions. From there, adjust based on how warm the room is, what season you’re in, and how your baby feels to the touch. Babies lose and gain heat faster than adults because of their high surface area relative to their body weight. A newborn has roughly 28% more skin surface per kilogram than a one-year-old, which means they cool down quickly in cold air and heat up quickly in warm environments.
Why Babies Need More Help Staying Comfortable
Newborns can’t shiver effectively, and while they’re born with a high density of sweat glands (about 6.5 times the density of an adult’s), their ability to regulate temperature through sweating is still maturing. The result is that young babies depend almost entirely on what you put on them and the temperature of the room around them. By around eight to nine months, a baby’s metabolic heat production peaks, meaning they actually generate more body heat per unit of skin than both newborns and older children. So the right amount of clothing shifts as your baby grows.
Indoor Temperature and Sleep Layers
The recommended room temperature for a sleeping baby is 16 to 20°C (roughly 61 to 68°F). In this range, a bodysuit (onesie) under a well-fitting sleep sack works well. If your room runs warmer than 20°C, a single lightweight layer like a short-sleeve bodysuit is enough, and in genuinely hot weather, just a diaper is fine.
If the room drops below 16°C, add an extra clothing layer underneath the sleep sack rather than piling blankets on top. Never double up on sleep sacks. Air trapped between two layers creates more warmth than either layer’s rating suggests, which raises the risk of overheating and SIDS.
Always remove hats indoors. Babies release a significant amount of heat through their heads, so covering them inside can cause overheating even when the room feels cool to you.
Understanding TOG Ratings on Sleep Sacks
TOG stands for Thermal Overall Grade and measures how much heat a fabric traps. A higher number means a warmer sleep sack. Here’s a general guide:
- Over 27°C (80°F): 0.2 TOG, essentially a single muslin layer
- 23–26°C (73–79°F): 0.5 TOG, lightweight cotton
- 21–23°C (68–73°F): 1.0 TOG, standard year-round weight
- 16–20°C (61–68°F): 2.5 TOG, cozy for cooler rooms
- Below 16°C (60°F): 3.5 TOG, the warmest option
These ratings assume your baby is also wearing a bodysuit or light pajamas underneath. If you’re dressing your baby in heavier clothing, you may need a lower TOG than the chart suggests. The goal is always to hit the right total warmth rather than maxing out every layer.
How to Check if Your Baby Is Too Hot or Cold
Touch your baby’s chest or the back of their neck. These areas give you the most accurate read. Hands and feet tend to run cool on babies, so don’t rely on them as your thermometer. If your baby’s chest feels hot or sweaty, remove a layer. If it feels cool to the touch, add one.
Signs your baby is overheating include flushed or red skin, damp hair, fussiness, and unusual sleepiness or sluggishness. Some babies overheat without visibly sweating, so skin temperature is a more reliable check than waiting to see perspiration. In serious cases, overheating can lead to heat exhaustion, with symptoms like a rapid or weak pulse and clammy skin. If your baby seems confused, weak, or is vomiting, that’s a medical emergency.
Dressing for Cold Weather Outings
Layer with several thin, light pieces rather than one heavy item. Thin layers trap warmth efficiently and let you peel one off if your baby gets too warm in a heated store or car. A good cold-weather setup is a bodysuit, a fleece or knit layer, and then a winter coat with a hood. Cover the ears with a hat made from a warm but lightweight material.
Car seats require special attention. Bulky coats create slack in the harness straps, which means the straps won’t hold your baby snugly in a crash. The National Highway Traffic Safety Administration recommends using lightweight fleece layers instead of puffy jackets in the car seat. For extra warmth, buckle the harness snugly first, then place a coat backward over the straps or drape a blanket on top.
Dressing for Hot Weather
Light-colored, loose-fitting, lightweight clothing is the goal. A single layer of breathable fabric is usually plenty. Add a wide-brimmed hat (without ties, to avoid a strangulation risk) and UV-protective sunglasses if your baby will tolerate them.
Babies under 12 months should stay out of direct sunlight when possible. Use a stroller umbrella or canopy for shade rather than draping a blanket over the stroller, which can trap heat inside. For babies six months and older, apply broad-spectrum sunscreen with at least SPF 30 to any exposed skin. Schedule regular breaks in the shade or in a cool indoor space, and watch for the overheating signs described above.
Choosing the Right Fabrics
Cotton is breathable and works well in moderate to warm weather. It’s the go-to for summer layers and everyday bodysuits. The limitation is that cotton doesn’t regulate temperature actively: once it gets wet with sweat, it stays damp and can chill your baby.
Merino wool is naturally thermoregulating, keeping babies warm in cold conditions and wicking moisture away in warmer ones. It works across seasons and is less likely to leave your baby clammy after sweating. It costs more than cotton, but for sleep layers and transitional weather, it earns its price. Avoid synthetic fabrics as a base layer against the skin, since they tend to trap heat without breathing well.
Quick Reference by Temperature
- Above 27°C (80°F): Diaper only, or a single lightweight bodysuit. Minimal sleep sack (0.2 TOG) if needed.
- 23–26°C (73–79°F): Short-sleeve bodysuit. Light sleep sack (0.5 TOG) for sleep.
- 20–23°C (68–73°F): Long-sleeve bodysuit or light pajamas. 1.0 TOG sleep sack.
- 16–20°C (61–68°F): Bodysuit plus pajamas or a footed sleeper. 2.5 TOG sleep sack.
- Below 16°C (60°F): Bodysuit, warm pajamas, and a 3.5 TOG sleep sack. Add a layer underneath before adding blankets on top.
These are starting points. Every baby runs a little warmer or cooler, so check that chest or neck after 10 to 15 minutes and adjust. The right outfit is the one where your baby’s torso feels comfortably warm, not hot or cool, and they settle without fussing.