Baby Sleeping Bag TOG Guide UK: Which TOG for Which Room Temperature

TOG stands for Thermal Overall Grade. It measures how much heat a fabric holds in. The higher the number, the warmer the sleeping bag. A 0.5 TOG bag is a thin single layer for hot nights. A 2.5 TOG bag is the quilted standard that covers most of the UK year.

TOG measures warmth, and warmth is what matters. A thin bag with a dense fill can hold more heat than a thicker bag with a loose one, so you cannot judge a bag by squeezing it. The number on the label is the useful information.

A TOG rating on its own tells you nothing, though. It only makes sense as one part of a three-part sum: the room temperature, the TOG of the bag, and the clothes your baby wears underneath. Change any one of the three and the other two need checking. That sum is what the rest of this guide walks through.

One honest caveat before the chart. TOG testing is not identical across brands. Two bags both labelled 2.5 TOG can sit at slightly different points of that rating, and each brand writes its temperature chart for its own fabric and fill. So treat the chart below as the general UK convention, and treat the chart printed on your bag's packaging as the final word for that bag. Where the two disagree, the brand's own chart wins.

The Lullaby Trust and the NHS recommend a room temperature of 16 to 20 degrees C for baby sleep. The standard UK guidance for matching a sleeping bag to the room looks like this:

Room temperature	TOG rating
27 degrees C and above	No sleeping bag
24 to 27 degrees C	0.5 TOG
20 to 24 degrees C	1.0 TOG
16 to 20 degrees C	2.5 TOG
Below 16 degrees C	3.5 TOG

Three things to hold alongside the table.

The boundaries are soft. At 20 degrees C, a 2.5 TOG with a light layer underneath and a 1.0 TOG with a warmer layer underneath can both be right. Some brands put the 1.0 TOG band at 21 to 23 degrees rather than 20 to 24. When you are between two options, pick the lighter one and check your baby's neck after half an hour. Overheating is a risk factor for SIDS, so slightly cool is the safer side to land on. A cool baby wakes and complains. That is your cue to add a layer.

A 3.5 TOG bag is a last resort. If your baby's room sits below 16 degrees C most nights, the better fix is usually a small amount of background heating to lift the room into the recommended range. Never add a blanket on top of any sleeping bag to make up the difference.

You do not need all four ratings. A 1.0 TOG and a 2.5 TOG cover most of the UK year, with clothing changes underneath doing the fine adjustment. Our sleeping bag buying guide covers which bags are worth the money and which safety marks to check.

The single most useful purchase in this whole subject is a room thermometer. A basic digital one costs a few pounds from any supermarket, and the Lullaby Trust recommends one in every room where your baby sleeps. Adults are unreliable thermometers. A room that feels cool to you under a duvet can be warm for a baby in a 2.5 TOG bag.

Where you put it matters:

• At cot level, near the cot. Heat rises and pools unevenly. The reading two metres away by the door is not the temperature your baby is sleeping in.
• Away from radiators, windows, and direct sunlight. All three skew the reading.

Check the temperature at the time your baby will be asleep. A room that reads 23 degrees at 7pm on a summer evening can drop to 18 by 2am, and a winter room can swing the other way when the heating comes on at 6am. If your heating is on a timer, the overnight low and the early-morning high are the numbers worth knowing. Dress your baby for the temperature the room will spend most of the night at, and let a lighter choice cover the warm hour rather than a heavier choice covering the cold one.

For the full picture on room temperature, including winter and summer strategies, see our baby room temperature guide.

The clothes under the bag are the adjustable half of the system. Here is a conservative starting point, using cotton layers:

Room temperature	Sleeping bag	What baby wears underneath
27 degrees C and above	None	Nappy only, or nappy and a thin cotton vest
24 to 27 degrees C	0.5 TOG	Nappy only, or a short-sleeved vest
20 to 24 degrees C	1.0 TOG	Short-sleeved bodysuit
18 to 20 degrees C	2.5 TOG	Long-sleeved bodysuit
16 to 18 degrees C	2.5 TOG	Long-sleeved bodysuit plus a light cotton sleepsuit
Below 16 degrees C	3.5 TOG	Cotton sleepsuit, with a vest underneath if needed

A few rules that sit over the whole table:

• Check your brand's own chart first. Most sleeping bag brands print a temperature and clothing guide on the packaging, written for that bag. It overrides this table.
• Cotton over fleece. A fleece sleepsuit inside a sleeping bag traps too much heat. Cotton breathes.
• No hats indoors, ever. Babies release excess heat through their heads. A hat during sleep raises overheating risk.
• Adjust by one layer at a time. If the room moves a couple of degrees, change one thing and check your baby's neck. Big swings in what they wear cause more waking than the temperature did.

Summer is where UK bedrooms leave the recommended range. Only around 5% of UK homes have air conditioning, and in a heatwave a south-facing bedroom or top-floor flat can hold 27 degrees or more well past midnight.

When the room is above 24 degrees C, move to a 0.5 TOG bag with a vest or just a nappy underneath. Above 27 degrees C, drop the bag altogether. A nappy alone, or a nappy with a thin cotton vest, is enough. It can feel wrong to put a baby down in so little, and it is the right call on a hot night.

Beyond the bag itself:

• Cool the room before bedtime. Curtains or blinds closed on the sunny side through the day, windows open once the outside air is cooler than the inside air.
• A fan helps, pointed at the wall rather than at your baby. It circulates air without blasting one spot.
• Never drape anything over the cot, and keep the cot away from windows and direct sun.
• Check the neck an hour after bedtime. Hot nights are when the check earns its keep.

Our hot weather sleep guide covers heatwave nights in full, including feeds, hydration, and what to do when the room will not cool down.

Most sleeping bags carry a minimum weight, commonly around 7lb (3.2kg). This is a safety line rather than a suggestion. Below the minimum weight, the neck opening is too large relative to the baby, and a baby whose head can slip down inside the bag is at risk of suffocation. Check the specific bag's limit, because minimums vary between brands and sizes.

The fit test at any age: with the bag fastened, you should be able to fit two fingers between the neckline and your baby's chest, and no more. The head must not be able to pass through the neck opening. Arms out, no hood, and never a weighted bag of any kind.

If your baby was premature or has a low birth weight, do not start a sleeping bag until they have reached the bag's minimum weight, and talk it through with your midwife, health visitor or GP first. Small babies are less able to regulate their own temperature in both directions, so the standard charts are written for babies bigger than yours. Your midwife can help you judge layers for your baby's actual size.

For newborns under the weight minimum, a well-fitted swaddle with a light blanket firmly tucked below shoulder height, or cellular blankets tucked in below the shoulders, are the Lullaby Trust-aligned alternatives. Stop swaddling at the first signs of rolling, usually between three and five months, and move to an arms-out bag.

Overheating is a risk factor for SIDS, which is why every range in this guide leans cool. The check takes ten seconds and works at any temperature: feel the back of your baby's neck, or their chest. Warm is right. Hot or sweaty means remove a layer or move down a TOG.

Do not judge by hands and feet. They run cool in babies because of immature circulation, and adding layers because of cold hands is one of the most common routes to an overheated baby. The neck and chest are the reading that counts.

Signs your baby is too hot:

• A hot or sweaty neck or chest
• Damp hair, especially at the back of the head
• Flushed red cheeks
• Rapid breathing
• Heat rash, small red bumps usually on the neck and chest
• Restless, unsettled sleep

If you find any of these, remove a layer, take the temperature reading, and recheck the neck after twenty minutes or so. If your baby is regularly waking up sweaty, our guide to baby sweating at night works through the causes, because the TOG is the usual culprit and occasionally it is something else.

Rapid breathing, a high temperature, floppiness or unusual drowsiness can also be signs of illness. If your baby seems unwell rather than just warm, contact your GP or call NHS 111. This page is sleep guidance, and it never overrides your instinct that something is wrong.

A correctly chosen TOG sits inside the wider safer sleep guidance from the Lullaby Trust and the NHS. Whatever the room temperature, these stay constant:

• Back to sleep, on a firm, flat, waterproof mattress, for every sleep.
• A clear cot. No loose blankets, duvets, pillows, quilts, bumpers or soft toys for babies under twelve months. The sleeping bag replaces bedding, so nothing goes on top of it.
• No hats or hoods indoors, and nothing that can cover your baby's head during sleep.
• Never a weighted sleeping bag, swaddle or blanket. The Lullaby Trust and NHS advise against all weighted sleep products for babies.
• Room-share for the first six months. Your baby sleeps in your room, in their own cot or Moses basket, day naps included.
• Remove outdoor layers when you come inside, even if your baby is asleep. A coat or snowsuit indoors overheats a baby quickly.
• Check for BS 8510 on the label when you buy. It is the British safety standard for children's sleep bags.

The pattern across this whole guide is the same one: a room thermometer, the right TOG for the reading, one sensible layer underneath, and a hand on the back of the neck. Four small habits, and the temperature side of safer sleep is handled.

If you are ready to choose an actual bag, our UK sleeping bag guide covers what to buy, what makes a bag safe, and why the cheap ones are usually fine.