Convert tog to GSM for any filling, or answer three questions to find exactly the right tog for your bed.
Opens a duvet search — we may earn a small commission, at no cost to you.
A quick reference for tog, the season it suits, and the rough GSM you'll see on the label. GSM varies by filling, so treat these as a guide.
| Tog | Best for | Feels | Down GSM | Synthetic GSM |
|---|
The short version, so you can buy with confidence.
Tog measures warmth — how well a duvet traps heat. It runs from about 1 (cool summer) to 15 (deep winter).
GSM (grams per square metre) measures the weight of the filling. More GSM usually means warmer, but only within the same filling type.
That's the catch: a 200 GSM down duvet can be as warm as a 400 GSM synthetic one, because down traps far more heat per gram. So always convert with your filling selected above.
No single formula works for every duvet, because warmth-per-gram depends on the fill power and construction. This tool uses the typical conversion ranges manufacturers publish for each filling, which gets you within the right band for shopping.
If a product lists both numbers, trust the label — use this to sanity-check it.
A 9–10.5 tog duvet is the classic all-rounder for a UK bedroom. If you want true year-round flexibility, look for an all-seasons (3-in-1) set — a 4.5 tog and a 9 tog that popper together into a 13.5 tog for winter.
Keep it lower than an adult's. A 4.0–4.5 tog duvet suits a child's bed for most of the year, with up to 7 tog in a cold winter room. For babies under 12 months use a tog-rated sleeping bag instead of a duvet.
Two duvets can share the same tog and still feel nothing alike in the hand. Tog measures warmth, not weight — so a 10.5 tog down duvet can weigh a third of a 10.5 tog hollowfibre one and keep you exactly as warm.
Down and feather trap more heat per gram, which is why they cost more, pack down smaller, and feel lighter on the bed. Synthetic fillings like microfibre and hollowfibre need more material to reach the same tog, so they're heavier and cheaper — and usually the better pick if you want something machine-washable or you're prone to allergies. Comparing two duvets? Convert both to GSM with the right filling selected above; it's the only fair way to see which is genuinely warmer.
As a rough rule for a UK bedroom: 3–4.5 tog for summer, 7–10.5 for spring and autumn, and 12–13.5 for winter. A 9 or 10.5 tog is the classic "leave it on all year" choice if you only want one — you just adjust what you wear and how the heating's set.
If your room swings a lot between seasons, an all-seasons set is the clever buy: a 4.5 tog and a 9 tog that popper together to make 13.5 for the coldest months. Three duvets in one, without the storage faff.
If you wake up kicking the duvet off, go a tog band lower than the season norm — a 7 tog in winter often beats a stuffy 13.5, especially with the heating on. Natural fillings like down and wool breathe better than synthetic too, shifting heat away instead of trapping it.
Cold sleepers can do the reverse: go up a band, and look for a higher fill-power down. It's warmer for its weight, so you stay toasty without being buried under something heavy.