Sleep Sack TOG & Nursery Temperature Picker

What TOG you need, by temperature

For a room at 69–74°F (21–23°C) — where most centrally heated or air-conditioned American houses sit — the answer is a 1.0 TOG sleep sack over a short-sleeve bodysuit. Warmer than that, 75–81°F (24–27°C), drop to 0.5 TOG; cooler, 61–63°F (16–17°C), go to 2.5 TOG over a bodysuit and a footed sleepsuit; and in the 64–68°F (18–20°C) band the manufacturers genuinely disagree with each other, which is why the picker above returns "1.0 or 2.5" instead of pretending there is one right answer.

The tool takes your nursery temperature in °F or °C, asks where your baby is in the swaddle transition, and gives you three things: the TOG band, the layer list that goes underneath it, and the safety rails that apply whatever the thermometer says. Everything runs in your browser, nothing is stored, and the whole band table is printed on the page so you can check our work.

The one thing to understand before you use the chart

The TOG-to-temperature mapping is a manufacturer convention, not pediatric guidance. That sentence is the most important one on this page, and almost nobody says it out loud.

No pediatric body publishes a TOG chart. The AAP does not. The NHS does not. The Lullaby Trust explicitly refuses to, and its reasoning is the most useful thing written on the subject: every product uses different materials in different proportions, the air trapped between layers changes the insulation significantly, and every baby is different.

So where does the chart come from? From the people who make the bags. We gathered four of their charts in October 2026 and they do not agree:

Look at the 1.0 TOG column. Its cold edge runs from about 64°F (Ergobaby) to the low 70s (Kyte Baby) — a spread of six or seven degrees for the same number on the same kind of label. That is why the bands in the tool above are a consensus midpoint and are labeled an estimate, and why the 64–68°F row is allowed to say two things at once.

TOG by temperature: the table

This is the same table the tool uses, and the same one in our longer guide to sleep sack TOG ratings and nursery temperature. Read the notes underneath before you print it.

Three notes, all of which matter more than the table.

One: the bands are exact and they do not overlap. A reading of 68.9°F is in the 1.0-or-2.5 row; 69.0°F is in the 1.0 row. We chose the edges deliberately so a thermometer sitting precisely on a line always lands somewhere defined rather than between two answers.

Two: the cold floor is 16°C, not 61°F. Those are not quite the same number — 16°C is 60.8°F — and the difference matters if you measure in Celsius, because the only authorities that publish a floor publish it as 16°C. Rounding it up to 61 would push a perfectly in-guidance UK nursery out of the band by two tenths of a degree, so the tool derives the floor from the Celsius figure instead.

Three: a cold room is not a TOG problem. If the thermometer is under 16°C, the fix is the thermostat. Stacking warmth onto a baby to compensate for a cold room pushes you toward the AAP's one-layer ceiling from the other direction, which is the thing all of this is trying to avoid.

What a TOG actually is

TOG is a real unit, not marketing shorthand. One tog equals 0.1 m²·K/W of thermal resistance. It was devised in 1946 by F. T. Peirce and W. H. Rees at the Shirley Institute in Manchester as a friendlier alternative to the SI unit, and it is measured on a Shirley Togmeter under BS 4745:2005, the British method for determining the thermal resistance of textiles. SGS, one of the labs that runs the test, gives the equivalence as 1 tog = 0.1 m²K/W = 0.645 clo.

Higher number, more trapped air, warmer baby. That is the whole concept, and what creates the number is construction rather than fabric name: whether there is a wadding layer sewn between the outer and the lining, and how thick it is.

Is TOG regulated in the United States? No. We went looking specifically, because this is widely misreported. There is no CPSC rule requiring a TOG value on infant sleepwear and none defining how one must be tested for a baby product sold in the States. TOG labeling here is a voluntary manufacturer convention imported from the UK.

The first US voluntary standard written specifically for these products, ASTM F3735, was approved on 1 February 2026 and covers wearable sleep products and garments with a swaddling feature for children up to two years. It addresses "suffocation, strangulation and choking hazards" through design, sizing, labeling and testing requirements — it sets no thermal rating at all. In the UK, children's sleep bags are covered by BS EN 16781:2018, which superseded the older BS 8510:2009; that too is a safety standard, not a warmth one.

So: use TOG to compare one product against another. Use the room and the layers to keep your baby comfortable. And treat the number on the label as a manufacturer's claim rather than a certified measurement.

The layering rule, and the step everyone skips

This one is not folk wisdom. It is in the AAP's 2022 policy statement, in these words: "In general, dress infants appropriately for the environment, with no >1 layer more than an adult would wear to be comfortable in that environment." The parent-facing version on HealthyChildren says the same thing more gently: "Your baby only needs one more layer than you would wear in the same environment to be comfortable."

Here is the step people skip. Count the sleep sack as one of those layers. If you are comfortable in a t-shirt, your baby is in a bodysuit and a sack — not a bodysuit, a footed sleepsuit, and a sack. The sack is not free.

The Lullaby Trust adds the detail that makes this concrete: a folded blanket provides twice the insulation. Layers compound in ways one TOG number cannot capture, which is another way of saying the layer underneath is the dial you actually turn. One bodysuit either way is a bigger change than you would think, and it costs nothing.

Why the UK and US numbers are different

This is where most articles quietly pick a number and pretend everyone agrees.

The AAP declines to name a room temperature, and says so explicitly. Its 2022 policy statement reads: "Although studies have demonstrated an increased risk of SIDS with overheating, the definition of overheating in these studies varies. Therefore, it is difficult to provide specific room temperature guidelines to avoid overheating." That is an honest position from the most-cited pediatric body in the country, and it is worth knowing that it declines to supply the number every sleep sack chart is built on.

The UK bodies do name one, and it is cooler than most American homes. The NHS advises keeping the room "at a temperature between about 16 to 20C" and monitoring it with a room thermometer. The Lullaby Trust gives the same range as a UK consensus view — and concedes that it "feels quite cold to a lot of people." That is roughly 61 to 68°F.

The commonly repeated American figure is 68 to 72°F (20 to 22°C). The Sleep Foundation is one of many sources citing it, attributing it to "experts" and to "some studies" — and that same page notes that the AAP gives no specific range. It is a reasonable, widely used band, but trace it back and it comes from sleep and consumer sources, not from a pediatric body.

The two ranges overlap at exactly one point: 68°F / 20°C. That is not a rounding coincidence; it is the top of one band and the bottom of the other. The tool above reports your room against both separately rather than averaging them into a range nobody actually publishes. If your nursery reads 71°F you will be told, accurately, that you are inside the US figure and above the UK one — and that the AAP has no opinion.

Taken together, the honest summary is a band of about 61 to 72°F (16 to 22°C), aimed cool rather than warm, with an actual thermometer in the room because guessing is unreliable.

One more seam worth seeing rather than papering over: the Lullaby Trust pairs its whole 16–20°C band with "light bedding or a lightweight well-fitting baby sleep bag," and says a baby "should only need to wear a nappy, vest and sleep suit to sleep in." Manufacturer charts put 2.5 TOG squarely inside that same band. Both cannot be exactly right. The chart is a starting point; your baby is the instrument.

Signs your baby is too warm

Overheating is the reason any of this matters. The AAP is direct about it: "Overheating can increase the risk of SIDS."

The signs it lists are short and specific: sweating, a hot chest, or flushed skin.

Hands and feet are the wrong test, and almost everyone reaches for them first. The NHS puts it plainly: "Check your baby's temperature by feeling their chest or the back of their neck. Do not worry if their hands or feet feel cool, this is normal." Hands and feet run cooler than the rest of the body as a matter of course; they are not a thermostat.

Two more things from the guidance that run against instinct. A baby who is unwell with a fever needs fewer bedclothes, not more. And no hats indoors — the AAP advises against placing hats on infants when indoors except in the first hours of life or in the NICU, weighing the questionable benefit for preventing hypothermia against the real risk of overheating. If the room is genuinely cold, add a layer under the sack or warm the room; do not cover the head.

Practical version: check the chest or the back of the neck once, about an hour after bedtime, and adjust the layer underneath rather than swapping the sack.

Never anything weighted

The internet will offer you a weighted sleep sack or a weighted swaddle as the fix for a baby who will not settle. Do not take it, at any TOG.

The AAP's 2022 policy is unambiguous that weighted blankets, weighted sleepers, weighted swaddles and other weighted objects should not be placed on or near a sleeping infant, and that "weighted swaddle clothing or weighted objects within swaddles are not safe and therefore not recommended." The CPSC's safe sleep guidance tells families the same thing. The tool above will never return a weighted product, and we work through the underlying evidence separately in are weighted sleep sacks safe.

If your baby genuinely only settles with pressure, that is a conversation with your pediatrician, not a purchase.

How to check a sleep sack actually fits

A TOG number tells you about warmth. It tells you nothing about the three things that make a sack safe, and fit is the first of them.

• The neck and the armholes. The Lullaby Trust's guidance is that sleeping bags should be well fitted, particularly around the neck and arms, so a baby cannot wriggle down inside. A shoulder that slips through an armhole is a route down into the bag.
• The shape at the top. A deeper, narrower neckline is a design feature worth comparing between sacks, because it keeps loose fabric away from the face.
• The size system. Most sacks are sized by weight, not age, and the Lullaby Trust's guidance is to go by the weight range on the label. A too-big 1.0 TOG sack is a worse buy than a well-fitting 2.5.
• The hips and legs. There should be room for the frog-legged position — legs free to bend up and out at the hip, the shape hip-health guidance asks for. Anything that holds the legs straight and together is the wrong shape.
• The zipper. A guard at the chin keeps the pull away from your baby's face, and a two-way or bottom-opening zipper is the detail you appreciate at 3 a.m. when you are changing a diaper without taking the whole bag off.

When a sleep sack is not the right answer

A few situations where the chart above does not apply.

Once your baby is attempting to roll, a swaddle is finished. The AAP's 2022 policy: "When an infant exhibits signs of attempting to roll (which usually occurs at age 3 to 4 months but may occur earlier), swaddling is no longer appropriate because it could increase the risk of suffocation if the swaddled infant rolls to the prone position." The trigger is a behavior, not a birthday — twisting the hips, arching, rocking side to side, getting up on one shoulder, or breaking an arm out of a swaddle that held fine last week. Any of it, once, counts. Our full walk-through is at when to stop swaddling, and what changes afterwards is at safe sleep after your baby rolls over.

A one-arm-out swaddle is still a swaddle. A gradual transition is something you do before signs of rolling appear, not a way to extend past them. Once rolling starts, both arms come out tonight.

A room above about 82°F. At that point the lightest bag made is still a layer, and the lever is the room: a fan, an open window, air conditioning. The tool flags this rather than recommending a thinner sack as though it solved the problem.

A room below 16°C. Same logic in reverse. Warm the room into the band, then dress for the band.

Anywhere the basics are not already right. A sack earns its place by getting the loose blanket out of the crib — the AAP's position is that dressing an infant in layers of clothing is preferable to blankets and other coverings, and that wearable blankets can also be used. It does nothing about the surface, the position or the clutter. If that part is still a work in progress, start with how to set up a safe sleep space and what does not belong in the crib.

How many TOGs do you actually need to own?

Most families need one, in two or three copies — not three weights in one copy each.

If your home holds a fairly steady temperature year-round, which many centrally heated and air-conditioned US houses do, 1.0 TOG covers the widest band of ordinary indoor temperatures and will carry you through almost the whole year. Buy the weight that matches the room you actually have, in enough copies that one is always clean, and only add a second TOG if your nursery genuinely swings across seasons. A second sack in a different weight is a smaller mistake than a wasted one.

When you are ready to pick a specific bag, the best baby sleep sacks works through the weights and sizes.

The bottom line

1. Put a thermometer in the room. Every source above says measure, not guess.
2. Aim cool — somewhere in 61–72°F (16–22°C), knowing the UK bodies sit at the bottom of that band and the common US figure sits at the top, and that the AAP names no number at all.
3. Pick the TOG for the room you have, not the season on the calendar.
4. Adjust with the layer underneath, not the sack.
5. No more than one layer more than you would wear — counting the sack — and no hat indoors.
6. Check the chest or the back of the neck, never the hands or feet.
7. Nothing weighted, ever.

The chart is a starting point, and we would rather say that out loud than let it read as a prescription. Tonight, do the free part: read the thermometer and feel the back of her neck.