The simplest rule: dress your baby in one layer more than you’d wear comfortably in the same room. For most homes kept between 68°F and 72°F, that means a onesie under a wearable sleep sack, or a footed sleeper on its own. Getting it right is less about following a rigid chart and more about understanding a few key principles around temperature, layering, and safe sleep.
The One-Layer Rule
Whatever you’re comfortable sleeping in, add one layer for your baby. If you’d sleep in a t-shirt, your baby does well in a bodysuit plus a lightweight sleep sack. If you’d want a blanket, bump up to a warmer sleep sack or add a long-sleeved layer underneath. This guideline works because babies lose heat faster than adults but also overheat more easily, since they can’t kick off covers or tell you they’re uncomfortable.
Loose blankets, quilts, and pillows don’t belong in the crib. A wearable sleep sack replaces a blanket safely and keeps your baby warm without the suffocation risk.
Room Temperature Sets the Starting Point
The recommended nursery temperature is 68°F to 72°F (20°C to 22°C). A simple room thermometer takes the guesswork out of this. Once you know the temperature, you can match clothing layers to it.
- 75°F to 81°F: A short-sleeve bodysuit or even just a diaper with a very lightweight sleep sack is enough.
- 68°F to 75°F: A bodysuit or footed pajamas with a light sleep sack.
- 64°F to 68°F: A long-sleeve bodysuit or footed pajamas under a mid-weight sleep sack.
- Below 64°F: Add an extra clothing layer underneath a warmer sleep sack rather than piling on blankets.
These ranges aren’t absolute. Every baby runs a little warmer or cooler, and different fabrics insulate differently. Use them as a starting framework and adjust based on how your baby actually feels.
Understanding TOG Ratings
Sleep sacks are rated by TOG, a measure of thermal resistance. A higher TOG number means a warmer product. Here’s the general breakdown:
- 0.2 TOG: Very lightweight, for rooms 75°F to 81°F
- 1.0 TOG: Light, for rooms 68°F to 75°F
- 2.5 TOG: Warm, for rooms 61°F to 68°F
- 3.5 TOG: Heavy, for rooms below 61°F
One important caution: don’t layer two sleep sacks on top of each other thinking you’re adding the TOG values together. Air gets trapped between the layers and creates significantly more warmth than either product alone, which raises the risk of overheating. The same applies to blankets. A single blanket folded in half counts as two blankets’ worth of insulation.
Why Overheating Is a Serious Concern
Overbundling, excessive bedding, head covering, and high bedroom temperatures all fall under what researchers call thermal stress for infants. These conditions are recognized risk factors for SIDS (sudden infant death syndrome). Babies regulate body temperature partly through their heads and faces, which is why covering those areas is particularly dangerous.
This doesn’t mean you need to keep your baby cold. It means erring slightly on the cooler side is safer than erring warm. A baby who’s a bit cool will fuss and let you know. A baby who’s overheating may become sluggish and less responsive, which is harder to detect at night.
How to Check If Your Baby Is Too Warm
Cold hands and feet are normal in babies and don’t reliably indicate that they’re underdressed. Their circulation to the extremities simply isn’t as developed yet. Instead, touch the back of their neck or their chest. Skin there should feel warm and dry, not hot, clammy, or sweaty.
Signs your baby may be overheating include flushed or red skin, damp hair, unusual fussiness or restlessness, and feeling hot to the touch on the torso. In more serious cases, a baby may seem unusually limp, sluggish, or confused. Sweating is a useful indicator, but babies can overheat without producing visible sweat, so don’t rely on that alone.
Fabric Choices That Help
Cotton is the classic choice for infant sleepwear. It’s breathable, soft, and widely available. Bamboo viscose has gained popularity because it wicks moisture well, feels silky, and helps regulate temperature in both warm and cool conditions. It’s also naturally hypoallergenic, which can matter for babies with sensitive skin. Fleece and polyester trap more heat, so they’re best reserved for genuinely cold rooms or layered carefully.
Whatever fabric you choose, make sure sleepwear fits snugly. Loose, flowing clothing can ride up over a baby’s face. Snug-fitting sleepwear is also exempt from the flame-retardant chemical requirements that apply to loose-fitting children’s pajamas, so it tends to be made with fewer treated fabrics.
No Hats Indoors
Once you’re home from the hospital, remove hats for indoor sleep. Babies release a significant amount of excess heat through their heads, and covering them prevents that natural cooling. A hat can also slip down over a baby’s face during sleep. This applies year-round, even in cooler homes.
Socks, Mittens, and Loose Items
Loose socks and separate mittens can come off during sleep and become a suffocation hazard if they end up near your baby’s face. If your baby scratches their face or you want to keep their hands warm, footed sleepers and onesies with fold-over cuffs are the safer alternative. They stay attached to the garment and can’t be pulled off and chewed on.
Cold fingers are not a reason to add mittens. As long as your baby’s chest and neck feel warm, cool hands are perfectly normal and not a sign they need more clothing.
Swaddling and When to Stop
Swaddling can help newborns sleep by dampening the startle reflex, that sudden arm-flinging motion that wakes them up. A proper swaddle wraps the arms snugly while leaving the hips loose enough to bend naturally. It counts as a layer, so factor it into your temperature calculations.
The critical transition point comes when your baby starts showing signs of rolling, which can begin as early as 2 months. Once a swaddled baby rolls onto their stomach, they can’t use their arms to reposition or clear their airway. The American Academy of Pediatrics recommends weaning off the swaddle at the first signs of rolling attempts, not after they’ve actually rolled.
Other signs it’s time to stop: your baby consistently breaks free of the swaddle, fights being wrapped, or has outgrown the startle reflex (typically around 4 to 5 months). Transitional products with one or both arms free can ease the shift. Most families move to a regular sleep sack at this stage.
Seasonal Adjustments
Summer and winter don’t change the principles, just the combinations. In summer, when your home may be warmer, a diaper with a 0.2 TOG sleep sack or a short-sleeve onesie alone may be all your baby needs. In winter, a long-sleeve bodysuit under a 2.5 TOG sleep sack covers most situations without needing extra blankets.
The room thermometer matters more than the season. A well-heated home in January may call for the same sleepwear as a mild night in September. Check the actual room temperature rather than dressing based on what it feels like outside.