Do I need a 3.5 tog sleeping bag for winter in the UK?

Does the NHS name 3.5 tog?

No. The NHS Best Start in Life safer-sleep page lists 2.5 / 1.0 / 0.5 only. 2.5 tog is the all-year bag for 16–20°C. The dressing-a-newborn page says a sleepsuit plus a bag (or a sheet and blanket) is usual in winter, and that you should check the manufacturer's recommendation for winter tog thickness. If the baby feels cold in a bag, add a layer of clothing, not extra blankets.

So "do I need 3.5?" is not a question the NHS answers with a yes or no. It is a question about the room you actually have and the °C range printed on a specific bag.

What do Which? and retailers say about 3.5 tog?

Which? also says sleeping bags should not be used until the baby weighs 4 kg, and to look for BS EN 16781:2018. Those are product limits on that article, not an NHS tog band.

What if the heating is off and the room is under 16°C?

The Lullaby Trust's cold-weather page is written for exactly this winter: cost of living, homes that are hard to hold at 16–20°C, and the temptation to wrap up. Their published moves are clothing and tog, not hats, hot-water bottles, duvets or a cot parked against a radiator.

1. 1
   Measure the sleep room Put a thermometer in the room where the baby sleeps. The Trust and the NHS both use 16–20°C as the guide. Which? repeats the NHS line that all-night heating is rarely necessary; if heating stays on, the Trust says keep it low and no higher than 20°C.
2. 2
   Read the bag's own °C range If you already own a 3.5 tog bag, use it only inside the temperatures printed on that product. If you own a 2.5 tog bag, the NHS pairing is 16–20°C; below that, the Trust's next step is extra clothing or a higher tog — not a blanket on top.
3. 3
   Add clothing, not loose bedding on a bag Vest plus sleepsuit under the bag is the usual step up. The Trust says one blanket doubled counts as two if you use blankets instead of a bag. Never add a duvet, quilt or weighted bag for a baby under one year.
4. 4
   Check the chest or neck Hands and feet run cold. If the chest is cold, add a layer or step up a tog. If the neck is sweaty, remove a layer — overheating is the risk the Trust keeps repeating in winter.
5. 5
   If you cannot heat the room The Trust points to debt and food-bank help on that same cold-weather page. Which? notes winter disconnection rules and the Priority Services Register for households with a young child. Those are bill routes, not a reason to use a hot-water bottle in the cot.

Can I put a blanket over a sleeping bag instead of buying 3.5 tog?

The Lullaby Trust's line is explicit: if you are using a baby sleeping bag, do not add extra blankets on top. Add clothing or choose a higher tog. The NHS says the same: no other bedding with a bag. Stacking bags is also out — two 1.0 tog bags are not 2.0 tog, because trapped air increases warmth.

If you use blankets instead of a bag, the Trust wants lightweight layers, feet-to-foot, tucked no higher than the shoulders. A doubled blanket counts as two. That is a different system. Do not mix it with a bag to avoid buying a thicker tog.

How do I decide without a MayTally chart?

You do not need a fourth grid. If the sleep room holds 16–20°C, the official lists point at 2.5 tog plus whatever clothing the baby's chest says is needed. If the room is under 16°C and stays there, the official winter advice is extra clothing or a higher-tog bag. Whether that higher tog is a 3.5 you already see on a JoJo or Which? table depends on that product's printed range — not on a seasonal headline.

In shortIn short: 3.5 tog is a retail thickness for cold rooms, not an NHS winter requirement. Hold 16–20°C if you can; below that, step up clothing or tog, never a blanket on the bag; then check the chest.