What this is about
Pick the sleep bag by the temperature of the room your baby sleeps in, not by the season printed on the box. A thermometer next to the crib tells you which bag to use tonight.
The bag and the clothes under it are one outfit. A 2.5 TOG bag in a room at 18°C (64°F) keeps a baby comfortably warm with a long-sleeve bodysuit, but pair that same bag with a fleece sleepsuit and the outfit becomes too warm.
What TOG means
TOG is the warmth number on a sleep bag's label. Higher is warmer. Most bags are 0.5, 1.0 or 2.5 TOG. Some makers also sell a 1.5 or a 2.0, and a 3.5 for cold rooms.
No number on yours? Look up the brand and model on the maker's website. Some wool bags give a room range instead of a TOG, so go by that range.
A puffy sleep bag is not necessarily a warmer one, and a bamboo 1.0 TOG bag can feel surprisingly thin in your hands. The number comes from measuring the fabric, so trust the label over your fingers.
Sleep bag: which TOG for which room?
28°C (82°F) and warmerNo bag
24–27°C (75–81°F)0.5 TOG
20–23°C (68–73°F)1.0 TOG
19°C (66°F) and colder2.5 TOGThe chart is for a crib or a bassinet. In your bed, your body warms your baby too, so dress a little lighter. For a nap in the stroller, dress for the weather outside. A sleep bag never goes in a car seat, because padding under the harness leaves the straps loose.
What goes under the bag tonight?
A sleep bag doesn't have to change every time the bedroom gets a little warmer or cooler. A lighter or warmer layer under it covers a few degrees either way, which helps on the night a diaper leaks and the only clean bag is the wrong one. Past that, change the bag.
Take a bedroom that sits at 20–23°C (68–73°F) through the week. The same 1.0 TOG bag works every night, over a long-sleeve bodysuit on the cooler nights and a short-sleeve one once the room reaches 22°C (72°F).
Look at the fabric, too. A thin cotton sleepsuit and a thick fleece one both have long sleeves, but under a bag the fleece one is a much warmer layer.
Will your bag work tonight?
Your room tonight
18°C 64°F
Move the thermometer to your room's temperature.
Long-sleeve bodysuit, 2.5 TOG Warm sleep bag. Right for this room.
Long-sleeve bodysuit
2.5 TOGWarm sleep bag
Right for this room.
A 2.5 TOG bag is right at 19°C (66°F) and colder.
Which sleep bag do you have?
Where does your baby sleep?
Which sleep bags you need
Most families need one or two TOGs, not all three.
Most of the year1.0 TOG
In a home kept at 20–22°C (68–72°F) all year, it's often the only TOG you need.
Cold winters2.5 TOG
Add one if the bedroom drops to 19°C (66°F) or colder in winter.
Hot summers0.5 TOG
Worth buying only where summer nights stay at 24°C (75°F) or warmer. Elsewhere, the 1.0 over just a diaper does the job.
In the TOG you use most, get two, so there's always a clean one.
A sleep bag also has to fit. Buy the size for your baby's weight now, not one to grow into. In a bag that's too big, your baby can slip down inside and the neckline rides up over the chin.
When your baby outgrows a bag, buy the next size in the TOG for the coming months. If your 2.5 TOG bag gets too small in spring, the next size will be worn all summer, so buy that one as a 1.0. The size calendar shows the month each new size comes up for your baby.
Bedtime check
Check the room
Read the thermometer next to the crib, not the one in the hall.
Pick the bag
The bag for that temperature, with a bodysuit or sleepsuit under it.
Zip up and check the neck
The neckline sits below the chin, so your baby can't slip down inside.
Into an empty crib
On the back, with nothing else in the crib. The bag replaces the blanket.
Questions parents ask
Why do TOG charts disagree?
Each maker tests its own fabrics and draws its own chart, so two brands can put the same TOG a degree or two apart. If your bag came with a chart, follow it, because it was made for that fabric.
Do I need a 3.5 TOG sleep sack?
Only if the bedroom stays below 16°C (61°F) at night. Above that, a 2.5 TOG bag over a footed sleepsuit is warm enough. In a room that cold, warm it a little if you can, or use a 3.5.
Do swaddles have a TOG too?
Many zip-up swaddles do, and a 1.0 TOG swaddle suits the same room as a 1.0 TOG bag. When swaddling stops at the first try to roll, a sleep bag of the same TOG takes over.
Can a baby overheat in a sleep sack?
Yes, in a bag too warm for the room or with too much under it, and getting too hot raises the risk of SIDS. Feel the chest or the back of the neck: if it's hot or sweaty, take a layer off or change to a lighter bag.
What TOG does a newborn need?
The same TOG as an older baby in the same room. A sleep bag fits once your newborn weighs enough for the smallest size, and until then a swaddle or sleepwear does the job.
Can I use two sleep bags at once?
No. Two 1.0 TOG bags don't make a 2.0: air trapped between them adds warmth of its own, and your baby can get too hot. On a cold night, use the warmer bag, or warmer clothes under the one you have.
What if the room cools down overnight?
Pick the bag for the temperature the room holds most of the night, not the warm hour at bedtime.
Do toddlers need a different TOG?
No. Going up a size doesn't mean going up a TOG. Toddler bags come in the same TOGs as baby bags, and some have legs for walking.
