Last updated: 7 July 2026
The short answer
A tog rating measures how warm a duvet is. More precisely, it measures thermal resistance, which is how well the duvet stops your body heat escaping. The scale runs from about 1 (cool and light, for summer) up to 15 (very warm, for a cold winter room). The higher the tog, the warmer the duvet.
What tog actually measures
Tog is a unit of thermal insulation. A high-tog duvet traps more of your body heat and lets less escape, so you feel warmer. A low-tog duvet lets heat move away more freely, so you stay cool. That is the whole idea. It says nothing about the size of the duvet, the material, or the quality, only how well it keeps warmth in.
One thing worth knowing is that tog is about the duvet, not the temperature of the room. Your ideal tog depends on how warm your bedroom is and how hot you personally sleep, which is why the same duvet can feel perfect for one person and stifling for another.
The tog scale
Duvets come in a handful of standard tog ratings. Here is what each band suits.
| Tog | Season | Feels |
|---|---|---|
| 1-4.5 | Summer | Light and cool |
| 7-9 | Spring and autumn | Light warmth |
| 10.5 | All year | Balanced |
| 12-13.5 | Winter | Cosy and warm |
| 15 | Deep winter | Very warm |
Opens an Amazon search, as an Amazon Associate we earn from qualifying purchases.
Tog vs GSM, what's the difference?
Tog and GSM measure two different things, and mixing them up is the most common duvet-buying mistake. Tog measures warmth. GSM (grams per square metre) measures the weight of the filling. They only line up within the same type of filling, because down traps far more heat per gram than synthetic. That is why a light 200 GSM down duvet can be just as warm as a heavy 400 GSM synthetic one. If a duvet lists a GSM instead of a tog, our tog to GSM converter translates between the two for any filling.
What tog is right for you?
For a typical UK bedroom, a 9 to 10.5 tog duvet is the all-year all-rounder. Choose a 4.5 tog for summer and a 13.5 tog for winter if you want the ideal for each season, or buy an all-seasons (3-in-1) set that clips together to cover the whole year. Run hot? Drop a level. Feel the cold? Go up one.
What about tog for babies?
Babies don't use duvets. Instead they use tog-rated sleeping bags, where the same idea applies but the numbers are lower, from 0.5 tog for warm rooms up to 3.5 tog for cold ones. Our baby sleeping bag tog guide covers this in full, including what to dress baby in.