What should my baby wear under a sleep sack?

It depends on the sleep sack's TOG rating and your room temperature. As a rule of thumb, dress your baby in no more than one extra layer than you would wear to be comfortable in that room. In a typical 68 to 72 degree nursery with a 1.0 TOG sack, a long-sleeve cotton bodysuit or footed pajamas underneath is usually right.

What TOG sleep sack do I need for my room temperature?

Match the TOG to the room: use 0.5 TOG for warm rooms around 74 to 78 degrees, 1.0 TOG for the common 69 to 73 degree range, and 2.5 TOG for cooler rooms around 61 to 68 degrees. If you fall between two ranges, choose the lower TOG and add a thin layer if needed, since overheating is the bigger safety concern.

How do I know if my baby is too hot in a sleep sack?

Check the chest or the back of the neck, not the hands or feet. Hands and feet often feel cool even when your baby is perfectly comfortable. Skin that feels hot, damp, or sweaty, along with flushed cheeks or rapid breathing, means your baby is too warm. Overheating raises the risk of SIDS, so remove a layer if you see these signs.

Can my baby wear footie pajamas under a sleep sack?

Yes, footed pajamas are a common and safe base layer under a sleep sack in cooler rooms, typically with a 1.0 TOG sack or higher. In a warm room, a footie plus a higher-TOG sack can be too much, so a short-sleeve bodysuit may be enough. Always do the chest check and skip socks and a hat indoors.

Should my baby wear socks or a hat under a sleep sack?

No. Babies should not wear a hat to sleep indoors because the head releases heat and covering it can lead to overheating. Socks are usually unnecessary too, since most sleep sacks cover the feet and cool feet alone do not mean your baby is cold. Use the chest check instead of relying on hands and feet.

What to Wear Under a Sleep Sack: TOG and Room-Temperature Chart

Creator: The newborn.mom team
Published: 2026-05-30

A simple TOG and room-temperature chart for what to dress your baby in under a sleep sack, plus the chest-not-hands overheating check and when to call your provider.

By The newborn.mom teamUpdated May 30, 20267 min read

Getting your baby dressed for sleep feels like it should be simple, but the sleep sack added a new variable: now you have to figure out what goes underneath. Too little and you worry your baby is cold. Too much and you risk overheating, which actually matters for safety. The good news is there is a straightforward way to get it right almost every night. You match the sleep sack's TOG rating to your room temperature, then add the correct base layer underneath, and you check your baby's chest to confirm. This guide gives you a simple chart, the one overheating check that beats feeling the hands, and clear signs for when to ask your provider.

Keep in mind that babies run a little warmer than adults and that comfort ranges are wide. You do not need a perfect number. You need a safe, reasonable layer and a quick way to double-check.

What TOG actually means

TOG stands for Thermal Overall Grade. It is just a measure of how warm a fabric is. A higher TOG sleep sack traps more heat. A lower TOG is lighter and cooler.

You will usually see four common ratings:

0.5 TOG: very light, for warm rooms or summer.
1.0 TOG: the all-rounder, good for most year-round nurseries.
2.5 TOG: warm, for cooler rooms or winter.
3.5 TOG: heaviest, for cold rooms only.

The TOG tells you the warmth of the sack itself. What you put on underneath does the rest of the work. Think of it as a two-part system: the sack plus the base layer should add up to the right amount of warmth for the room.

A quick reality check before the chart: the safest nursery temperature for sleep sits around 68 to 72 degrees Fahrenheit. The American Academy of Pediatrics recommends keeping the room at a temperature comfortable for a lightly clothed adult and warns that overheating raises the risk of SIDS, so the goal is always "warm enough," not "as warm as possible" AAP, healthychildren.org.

The TOG and room-temperature chart

Find your room temperature, then pair the TOG with the base layer. If you land between two rows, size down on warmth. It is safer to be slightly cool than too hot, and you can always add a thin layer.

Warm room: 74 to 78 degrees F

TOG: 0.5
Wear underneath: just a diaper, or a short-sleeve bodysuit.

Comfortable room: 69 to 73 degrees F

TOG: 1.0
Wear underneath: a long-sleeve bodysuit, or footed pajamas in the cooler part of this range.

Cool room: 64 to 68 degrees F

TOG: 1.0 to 2.5
Wear underneath: footed pajamas, or a long-sleeve bodysuit plus footed pajamas with a 2.5 TOG sack.

Cold room: 61 to 64 degrees F

TOG: 2.5 to 3.5
Wear underneath: footed pajamas, sometimes with a long-sleeve bodysuit layered under them.

A few notes that save second-guessing. Skip socks once your baby is in a sack, since the sack covers the feet. Skip a hat entirely for indoor sleep. And do not add a loose blanket on top of any sleep sack. The sack is the blanket. Loose bedding in the sleep space is exactly what wearable blankets are designed to replace AAP, healthychildren.org.

The chest check beats the hands

Here is the single most useful habit. To tell if your baby is dressed right, feel the chest or the back of the neck, not the hands or feet.

Babies often have cool hands and cool feet even when the rest of them is perfectly comfortable. That is normal circulation, not a sign your baby is cold. If you dress your baby based on cold hands, you will almost always overdress.

The chest should feel warm and dry. If it feels hot, damp, or sweaty, your baby is too warm and you should remove a layer. The AAP notes that a baby may be too hot if they are sweating or their chest feels hot AAP, healthychildren.org.

Other signs of overheating to watch for:

Flushed or red cheeks.
Damp hair or a sweaty neck.
Rapid breathing.
Restlessness or fussiness that improves when you cool the room or remove a layer.

This matters beyond comfort. Overheating and overbundling, meaning too many layers for the room, are recognized risk factors for SIDS Safe to Sleep, NICHD. When you are deciding between warmer and cooler, that is why the safer default is cooler.

The simple rule when you have no chart handy

If you are traveling, half-asleep at 3 a.m., or just do not want to think about TOG numbers, use this: dress your baby in no more than one extra layer than you would need to be comfortable in that same room AAP, healthychildren.org.

So if you would be comfortable in a long-sleeve shirt, your baby can wear a base layer plus the sleep sack, which is roughly one extra layer of warmth. If the room is warm enough that you would be fine in a t-shirt, lean toward a short-sleeve bodysuit and a light sack.

This rule travels well and it forgives a lot. It also keeps you from the common trap of treating the sleep sack as the only layer or as an extra blanket on top of an already warm outfit.

Adjusting for seasons and growth

Your nursery is not the same temperature in January and July, so your layering should shift too. The chart still works. You just move up or down the rows as the room changes.

In summer, a 0.5 TOG sack with only a short-sleeve bodysuit, or even just a diaper in a hot room, is often plenty. Running a fan can help, and good airflow is associated with safer sleep. In winter, a 2.5 TOG sack with footed pajamas underneath usually covers a cool room without piling on layers.

Watch the room, not the calendar. A heated apartment in winter can be warmer than a breezy house in summer. A small room thermometer near the crib, not in direct sun or airflow, takes the guesswork out.

As your baby grows, two things change. First, your baby starts regulating temperature a little better. Second, and more important, once your baby shows signs of rolling, you move out of swaddles and into arm-free sleep sacks, which can feel slightly cooler since the arms are out. You may bump the base layer to long sleeves to compensate, then do the chest check to confirm.

When to call your provider

Most temperature questions are about comfort, not emergencies, and the chest check resolves the great majority of them. Still, call your pediatrician or seek care if you notice any of the following:

A rectal temperature of 100.4 degrees F or higher in a baby under 3 months. This is always a reason to call right away, regardless of how your baby is dressed.
Your baby feels hot, sweaty, or limp and does not cool down after you remove a layer and move them to a cooler room.
Persistent rapid breathing, unusual sleepiness, or trouble waking.
Cool, mottled, or bluish skin that does not improve in a warm room.

You know your baby. If something feels off and dressing changes do not fix it, trust that instinct and reach out. Providers would much rather answer a layering question than have you worry through the night.

Frequently asked questions

What should my baby wear under a sleep sack?: It depends on the sleep sack's TOG rating and your room temperature. As a rule of thumb, dress your baby in no more than one extra layer than you would wear to be comfortable in that room. In a typical 68 to 72 degree nursery with a 1.0 TOG sack, a long-sleeve cotton bodysuit or footed pajamas underneath is usually right.
What TOG sleep sack do I need for my room temperature?: Match the TOG to the room: use 0.5 TOG for warm rooms around 74 to 78 degrees, 1.0 TOG for the common 69 to 73 degree range, and 2.5 TOG for cooler rooms around 61 to 68 degrees. If you fall between two ranges, choose the lower TOG and add a thin layer if needed, since overheating is the bigger safety concern.
How do I know if my baby is too hot in a sleep sack?: Check the chest or the back of the neck, not the hands or feet. Hands and feet often feel cool even when your baby is perfectly comfortable. Skin that feels hot, damp, or sweaty, along with flushed cheeks or rapid breathing, means your baby is too warm. Overheating raises the risk of SIDS, so remove a layer if you see these signs.
Can my baby wear footie pajamas under a sleep sack?: Yes, footed pajamas are a common and safe base layer under a sleep sack in cooler rooms, typically with a 1.0 TOG sack or higher. In a warm room, a footie plus a higher-TOG sack can be too much, so a short-sleeve bodysuit may be enough. Always do the chest check and skip socks and a hat indoors.
Should my baby wear socks or a hat under a sleep sack?: No. Babies should not wear a hat to sleep indoors because the head releases heat and covering it can lead to overheating. Socks are usually unnecessary too, since most sleep sacks cover the feet and cool feet alone do not mean your baby is cold. Use the chest check instead of relying on hands and feet.