A newborn should sleep in one layer more than what you’d wear comfortably in the same room. In most homes, that means a short-sleeve bodysuit (onesie) under a swaddle or lightweight sleep sack, with no hats, no loose blankets, and no extra bedding. The specifics depend on your room temperature, which should stay between 68°F and 78°F.
Start With Room Temperature
Before picking out sleepwear, check the temperature in your baby’s room. A thermometer near the crib gives you a reliable baseline. The comfortable range for a nursery is 68°F to 78°F, with most pediatric sources landing around 68°F to 72°F as the sweet spot. A fan on low can help keep air circulating, which also reduces the risk of SIDS.
Once you know the room temperature, you can match your baby’s clothing to it rather than guessing. Overdressing is more common (and more dangerous) than underdressing, so when in doubt, go lighter.
What TOG Ratings Mean for You
TOG stands for Thermal Overall Grade. It’s a number printed on sleep sacks and wearable blankets that tells you how warm the fabric is. Higher TOG means warmer. Here’s how it breaks down by room temperature:
- 0.2 TOG: Best for 75°F to 81°F. This is essentially a single layer of thin fabric.
- 1.0 TOG: Best for 68°F to 75°F. The most common choice for temperature-controlled homes.
- 1.5 TOG: Best for 64°F to 72°F. Good for slightly cool rooms.
- 2.5 TOG: Best for 61°F to 68°F. Suited to colder homes in winter.
- 3.5 TOG: Best for rooms below 61°F.
If your nursery sits at 70°F to 72°F, a 1.0 TOG sleep sack over a short-sleeve onesie is a reliable combination. On warmer nights above 75°F, you might use just a onesie with a 0.2 TOG sack, or skip the sack entirely and dress your baby in a single-layer footed sleeper.
Layering for Common Temperatures
The one-layer-more rule is the simplest guide. If you’d sleep in a T-shirt and feel comfortable, your baby needs roughly that plus one light layer on top. Here’s what that looks like in practice:
- Above 75°F: A short-sleeve onesie alone, or a onesie with a very lightweight (0.2 TOG) sleep sack.
- 68°F to 74°F: A short-sleeve or long-sleeve onesie under a 1.0 TOG sleep sack.
- 61°F to 67°F: A long-sleeve onesie or footed pajama under a 2.5 TOG sleep sack.
- Below 61°F: A long-sleeve onesie layered under footed pajamas, plus a 2.5 to 3.5 TOG sleep sack.
Avoid piling on multiple blankets or thick clothing. Each additional layer traps more heat, and newborns can’t regulate their body temperature the way adults can. Adding layers gradually and checking your baby’s comfort is safer than starting heavy and hoping for the best.
Swaddles, Sleep Sacks, and When to Switch
For the first few months, many parents swaddle their newborn with arms snug against the body. Swaddling can reduce the startle reflex that wakes babies up, and most newborns sleep more soundly wrapped up. A purpose-made swaddle wrap with velcro or zippers is easier and safer than a loose blanket.
The swaddle has an expiration date. Once your baby shows signs of rolling over, typically between 3 and 4 months, the swaddle needs to go. When a baby rolls onto their stomach, they need their arms free to push up from the mattress. If your baby can get their body up onto one shoulder, that’s a rolling sign, and it’s time to transition.
The next step is a wearable blanket, often called a sleep sack. These zip on like a little sleeping bag with arm holes, giving your baby warmth without any loose fabric in the crib. Sleep sacks come in different TOG ratings, so you can match them to your room temperature year-round. Many parents start with a transitional sack that lets one arm out at a time before going fully arms-free.
Fabrics That Work Best
Cotton and bamboo are the two best materials for newborn sleepwear. Both are breathable, naturally temperature-regulating, and gentle on sensitive skin. Organic cotton is durable, easy to wash, and keeps babies cool without losing softness over time. Bamboo is naturally moisture-wicking, meaning it pulls sweat away from the skin, which makes it especially popular for sleep sacks and footed sleepers.
Synthetic fabrics like polyester and fleece can trap heat and moisture against your baby’s skin, leading to irritation and discomfort. Fleece sleep sacks exist and may seem cozy, but they’re harder to pair correctly with other layers because they retain so much warmth. If you do use fleece for very cold rooms, dress your baby in fewer layers underneath and monitor closely for overheating.
No Hats Indoors
The American Academy of Pediatrics is clear on this: do not place hats on babies indoors, except during the first hours after birth or in the NICU. A hat prevents heat from escaping through the head, which is one of the main ways a newborn releases excess body heat. Indoors, a hat can cause dangerous overheating without obvious warning signs. Save beanies for outdoor trips in cold weather.
How to Tell If Your Baby Is Too Hot
Touch the back of your baby’s neck or their chest. These areas give a more accurate read on core temperature than hands or feet, which tend to feel cool even when a baby is perfectly warm. If the skin on their neck or chest feels hot or clammy, they’re overdressed.
Other signs of overheating include flushed or red skin, damp hair, fussiness, and unusual sleepiness or sluggishness. Heat rash, which looks like tiny red bumps in skin folds, around the neck, and on the bottom, is another clear signal. Babies can overheat without sweating, so don’t rely on sweat alone as your indicator. If your baby seems too warm, remove a layer and check again in 10 to 15 minutes.
What Not to Put in the Crib
Loose blankets, pillows, stuffed animals, bumper pads, and positioning devices do not belong in a newborn’s sleep space. The safest crib has a firm, flat mattress with a fitted sheet and nothing else. All warmth should come from what your baby is wearing, not from bedding draped over them. This applies to bassinets, pack-and-plays, and any other sleep surface.
If your baby’s sleepwear is properly matched to the room temperature, loose blankets become unnecessary. A well-chosen sleep sack does the same job without the suffocation risk.