Baby Sleeping Bag TOG Guide: Which TOG, Which Size, and Until What Age

The TOG rating says nothing about what your baby wears underneath. A 2.5 TOG sleeping bag over thick pajamas is much warmer than the same bag over a simple bodysuit. What matters for your baby is the total warmth: sleeping bag plus clothing. Parents often mix the two up, and that is how a baby ends up overdressed.

A higher TOG is not a better or safer product. It is simply meant for a colder room. A 0.5 TOG sleep sack is just as safe as a 3.5 TOG one when it is used at the right temperature.

Which TOG for which room temperature?

Choose the TOG from the temperature measured in the nursery, not from the season or the weather outside. A simple room thermometer placed near the crib is enough. The NHS recommends a room between 16 and 20°C (61 to 68°F) for a sleeping baby.

Here is the baby sleeping bag TOG chart most manufacturers use:

Rooms at 18 to 20°C (64 to 68°F) are the most common in winter. There, a 2.5 TOG sleeping bag over a long-sleeved bodysuit is usually enough. For a detailed, degree-by-degree outfit guide, see our article on how to dress your baby for sleep by room temperature. To set up the room itself, read our guide to the ideal baby room temperature for sleep.

In practice, two sleeping bags cover most situations: a 1 TOG for summer and warm rooms, and a 2.5 TOG for the rest of the year. A 3.5 TOG is only useful in a genuinely cold room.

What the science says about sleeping bags and overheating

Studies link the baby sleeping bag to safer sleep, and link overheating and a covered head to a higher risk of sudden unexpected infant death. So choosing a TOG is not only about comfort. The right TOG avoids a cold baby and, above all, an overheated one.

The sleeping bag as a protective factor

A case-control study in the Netherlands compared the sleep habits of babies who died suddenly and unexpectedly with those of control babies (L'Hoir et al., 1998). The duvet, which can cover the head and body, was among the risk factors. The cotton sleeping bag was among the protective factors.

A covered head: a major risk

A systematic review of 10 studies looked at whether the baby's head was covered during the last sleep (Blair et al., 2008). It was the case for 24.6% of the babies who died, against 3.2% of control babies. The authors conclude that head covering is a major and avoidable risk factor. A sleeping bag with a snug neck opening is precisely what stops a baby from slipping down inside.

Too many layers, too warm

A British study published in the BMJ showed that overheating is a risk factor independent of sleep position (Fleming et al., 1990). The babies concerned were more often heavily wrapped, with very insulating clothing and bedding, and more often in a room heated all night. The effect was stronger after 70 days of age.

The American Academy of Pediatrics also recommends avoiding overheating and not covering the baby's head (Moon et al., 2022). It advises against weighted sleep sacks, weighted swaddles and weighted blankets, which are not safe for infant sleep.

Keep the key idea in mind: when in doubt, a baby dressed slightly too lightly is safer than a baby dressed too warmly. To understand how your baby regulates heat, see our article on infant thermoregulation and body temperature during sleep.

How to choose a baby sleeping bag: size, neck, armholes, sleeves, feet, zip, safety standard

A good baby sleeping bag is above all the right size: snug at the neck and armholes, roomy around the legs. Then come the TOG, the fabric and the options. Here are the points to check before you buy.

Sleep sack size and neck opening

This is the number one safety point. The neck opening and armholes should be snug, so your baby's head cannot slip inside the bag. Buying a sleeping bag that is too big "so it lasts longer" is a false saving. Follow the manufacturer's weight and height range rather than age alone. Sizes such as 0-6 months, 6-18 months and 18-36 months are only a rough guide.

Room for the legs and hips

The bottom of the sleeping bag should let your baby bend their legs up and out freely. This matters for healthy hip development. A bag that is too narrow restricts this natural position.

Sleeveless or with sleeves

Sleeveless sleeping bags suit most situations. Long sleeves can help in a cool room, as long as you reduce the layers underneath. Be aware that sleeves add warmth: a 2.5 TOG sleeping bag with sleeves is warmer than the same bag without them.

With or without feet

Sleeping bags with feet, sometimes called sleep suits or walking sleep sacks, suit toddlers who walk. They let a child stand up in the crib without tripping. For a baby who is not walking yet, the classic bag shape is the simplest option.

Fabric and zip

Choose a breathable fabric, such as cotton. A side or front zip makes night-time diaper changes easier. Check that the zip has a fabric guard at the top so it does not rub the chin.

Safety standard

In Europe, children's sleeping bags are covered by a safety standard, EN 16781. It sets rules for the size of the neck opening and armholes, among other things. Look for it on the label or the product page. In the US, there is no single TOG standard, so check the manufacturer's temperature guidance and fit chart.

What to avoid

• Weighted sleep sacks and weighted swaddles, advised against by the American Academy of Pediatrics.
• Sleeping bags with a hood, or anything that covers the head.
• Second-hand sleeping bags that are stretched out or too big.
• A blanket or duvet added on top of the sleeping bag.

Swaddle, sleeping bag, blanket: when to switch?

Move from a swaddle to a sleeping bag as soon as your baby shows signs of trying to roll over, often around 2 to 4 months. The sleeping bag can then stay with your baby until 2 or 3 years old, often until the move to a big bed. Blankets and pillows do not come before 12 months.

From swaddle to sleeping bag

A swaddled baby who rolls onto their tummy cannot use their arms to get back onto their back. That is why swaddling stops at the first attempts to roll. Some transition sleep sacks free one arm first, then both. Our guide on when to stop swaddling your baby explains the signs to watch for.

From sleeping bag to blanket

The NHS advises against duvets and pillows before 12 months. Many families keep the sleeping bag much longer, until the child leaves the crib. When you do switch to a blanket, choose a light one and tuck it in under your child's arms.

How to tell if your baby is too hot or too cold

Feel the back of your baby's neck or their chest: it is the best guide, far more reliable than their hands or feet. A neck that is warm and dry means all is well. A neck that is damp or hot means your baby needs fewer layers.

A baby's hands and feet often feel cool. This is normal and does not mean your baby is cold. On the other hand, these signs show that your baby is too hot:

• a sweaty neck or back;
• damp hair;
• very red cheeks;
• fast breathing;
• restlessness.

If you notice them, remove a layer of clothing or switch to a lower TOG sleeping bag. Never put a hat on your baby for sleep indoors: babies lose a lot of their heat through the head.

Following several nights can also help you see whether the TOG you chose suits your baby. The Mothair smart mattress topper sits on the mattress, under the fitted sheet, and works with a normal sleeping bag. It tracks temperature and movement during sleep, contact-free (how contactless monitoring works). It does not replace the simple habit of feeling your baby's neck.

When to see your pediatrician

See your pediatrician if your baby sweats a lot at night even though they are not overdressed, or if they have a fever. A fever in a baby under 3 months always needs prompt medical advice. If your baby has a fever, do not add layers: lighten their clothing and their sleeping bag.

Ask for advice too if your baby was born premature or with a low birth weight. Standard sleeping bag sizes can be too big, and smaller sizes exist.

Important: Mothair is a wellness device and is not a medical device. This article is for information only and does not replace medical advice. Consult your pediatrician with any question about your baby's sleep or health.

FAQ

What TOG sleeping bag for a room at 18-20°C (64-68°F)?

A 2.5 TOG sleeping bag suits a room between 16 and 20°C (61-68°F), worn over a long-sleeved bodysuit. If your baby's neck feels damp, lighten the layer underneath. Above 20°C (68°F), switch to a 1 TOG sleeping bag.

Are weighted sleep sacks safe?

No. The American Academy of Pediatrics advises against weighted sleep sacks, weighted swaddles and weighted blankets for infant sleep. Choose a regular, non-weighted sleeping bag with the right TOG for the room.

How should a baby sleeping bag fit?

Follow the manufacturer's weight and height range rather than age alone. The neck opening and armholes should be snug so your baby's head cannot slip inside the bag. The bottom should stay roomy so your baby can bend and move their legs freely.

Until what age should a baby use a sleeping bag?

Many children use a sleeping bag until 2 or 3 years old, often until they move to a big bed. Duvets and pillows are not recommended before 12 months. For toddlers who walk, sleeping bags with feet are available.

Can I put a blanket over a sleeping bag?

No. The sleeping bag replaces the blanket. Adding a blanket increases the risk of overheating and of the head becoming covered. If your baby is cold, choose a higher TOG or add a layer of clothing underneath.

What is the difference between a sleep sack and a wearable blanket?

None. Sleeping bag (UK), sleep sack and wearable blanket (US) all describe the same product: a sleeveless or sleeved bag, closed at the bottom, that keeps a baby warm without loose bedding.

Conclusion

A baby sleeping bag is a simple ally for safe sleep: it keeps your baby warm with nothing that could cover their head. To choose one, three criteria are enough: a TOG that matches the temperature measured in the room, a snug fit at the neck and arms, and clothing underneath that goes with the TOG. And when in doubt, feel the back of the neck: it tells you whether your baby is too hot.