I’ve no notion about TOG.
I’m on a winters night protected by 13 point five TOG regime .
And these days…..
There are three measurement for ones duvet, 3.5, 7.5 and 13.5. These correspond with Summer, Autumn and Spring and the 13.5 for winter. But they are utterly meaningless for they are measuring something that you couldn’t care less about. It’s like having a measurement for road temperature when what you need to know is that the tyre will stop you.
And anyway there are nights in Winter when the accumulated 25tog would not be enough, while Summer nights that a sheet would be too much.