TOG Ratings Explained: What 0.5, 1.0, 2.5 and 3.5 Mean for Baby Sleep

If you have ever stood over a crib at 10pm holding two sleep sacks and wondering which one is right, this guide is for you. TOG is one of those baby-product numbers nobody explains — it just shows up on the label and you are expected to know.

Here is the short version: TOG stands for Thermal Overall Grade. It measures how warm a fabric is. The higher the number, the warmer the sack. That is genuinely all it is.

The rest of this guide covers what each rating means, what to put on underneath, and how to tell whether you got it right. If you would rather skip straight to an answer, our TOG calculator will tell you what to use for your nursery temperature.

The quick answer

Take your nursery's temperature, then match it:

Room temperature	TOG rating
75°F / 24°C and above	0.5 TOG
70–75°F / 21–24°C	1.0 TOG
61–70°F / 16–21°C	2.0–2.5 TOG
Below 61°F / 16°C	3.5 TOG

Use an actual thermometer in the nursery rather than the hallway thermostat. Bedrooms run warmer or cooler than the rest of the house, and upstairs nurseries in summer are often several degrees above whatever the thermostat claims.

What each TOG rating actually means

0.5 TOG — hot rooms and high summer

Barely more than a sheet. This is what you want when the nursery sits at 75°F or above and you still want the safety benefit of a sack instead of a loose blanket. Underneath: a short-sleeve bodysuit, or just a diaper if the room is genuinely hot.

1.0 TOG — warm rooms, and the one most people need in summer

Light but not flimsy. Good for 70–75°F, which covers most air-conditioned homes from June to September. Underneath: a short-sleeve bodysuit.

2.0 and 2.5 TOG — the year-round workhorse

If you only buy one sack, buy this one. It covers 61–70°F, which is where most nurseries sit for most of the year, and it matches the 68–72°F range paediatric guidance recommends for infant sleep. Underneath: a long-sleeve bodysuit, or a footed sleeper if the room is at the cooler end.

You will see both 2.0 and 2.5 on labels. The difference is small enough that they are used interchangeably by most parents — treat them as the same band.

3.5 TOG — genuinely cold rooms

For nurseries below 61°F: old houses, uninsulated rooms, winter in a cold climate. Underneath: warm footed pyjamas. If you are reaching for 3.5 TOG in a room that is only slightly cool, you are probably overdressing — go 2.5 and add a layer underneath instead, which gives you more control.

What goes underneath is half the answer

This is the part the TOG number does not tell you, and it is where most of the guesswork actually lives. A 1.0 TOG sack over a long-sleeve footed sleeper is warmer than a 2.5 TOG sack over a bare chest.

A workable rule: the sack sets the baseline, the layer underneath does the fine-tuning. Rather than owning four sacks, own one or two and change what goes under them. Cheaper, and easier to adjust when the weather turns overnight.

• Warm room: short-sleeve bodysuit
• Average room: long-sleeve bodysuit
• Cool room: footed sleeper, ideally breathable cotton or bamboo

How to tell if you got it right

Do not check your baby's hands or feet. Babies have poor circulation to their extremities and cool hands are normal — this single misunderstanding is responsible for an enormous amount of overdressing.

Check the chest or the back of the neck instead. Slide two fingers under the sleepwear:

• Warm and dry — you got it right.
• Damp or sweaty — too warm. Drop a TOG level, or remove the layer underneath.
• Cool to the touch — add a layer underneath before you reach for a heavier sack.

The most useful time to check is the small-hours wake-up, when the house is at its coldest and you are in there anyway.

Swaddle or sleep sack?

These are not the same thing, and the difference matters more than the TOG number.

A swaddle wraps the arms. It suits newborns, whose startle reflex wakes them constantly. A sleep sack leaves the arms free and works like a wearable blanket.

The switch point is not an age — it is a milestone. Stop swaddling the moment your baby shows any sign of rolling, even the earliest attempt. A swaddled baby who rolls onto their front cannot push back up. Most babies reach this between two and four months, but some get there earlier, so watch your baby rather than the calendar.

A note on weighted sleep sacks

You will see weighted sacks and weighted swaddles marketed for better sleep. Parents ask us about these often, so we will be direct: the American Academy of Pediatrics advises against weighted blankets, weighted swaddles and weighted sleep sacks for infants. Their safe-sleep guidance is explicit on the point.

We would rather tell you that than sell you something on a claim we cannot stand behind. If your baby is sleeping badly, room temperature and the layer underneath are the two things worth adjusting first, and they cost nothing to try.

Five mistakes worth avoiding

1. Dressing for the thermostat, not the nursery. Put a thermometer in the room.
2. Judging temperature by hands and feet. Check the chest.
3. Adding a loose blanket on top of a sack. The sack replaces the blanket — that is the entire point of it.
4. Buying a sack that is too big so it lasts longer. A baby can slip down inside an oversized sack. Check the size guide and buy for now.
5. Overdressing "just in case". Overheating carries more risk than being slightly cool, and a slightly cool baby will tell you about it.

Common questions

What does 1.0 TOG mean?
A lightweight sack suited to rooms between 70 and 75°F (21–24°C), worn over a short-sleeve bodysuit.

What does 2.5 TOG mean?
A mid-weight sack for rooms between 61 and 70°F (16–21°C) — the most useful single weight for year-round use in most homes.

What room temperature is right for a baby?
Paediatric guidance generally puts the range at 68–72°F (20–22°C).

Can my baby wear a sleep sack all year?
Yes — change the TOG rating and the layer underneath as the seasons turn, rather than abandoning the sack.

What TOG for 68°F?
2.0–2.5 TOG, over a long-sleeve bodysuit.

Work it out for your room

Rather than memorising the table, put your nursery temperature into the TOG calculator and it will give you the rating and what to layer underneath.

When you know your number, our sleep sacks are organised so you can filter to it, and every one is chosen the same way we choose everything here — by a family who has done the 2am chest-check more times than we can count.