UK duvet sizes

Note that a double duvet is square, at 200 by 200. That is the only UK size where the width and length match, and it catches people out when putting a cover on.

Why one size up works

A duvet sized exactly to the bed has no overhang, so it sits on top of the mattress rather than draping over the sides.

Two consequences. Warm air escapes at the edges, which is felt as a cold draught down one side, and people respond by buying a warmer duvet when the problem was coverage rather than tog. And on a shared bed it gets pulled, because there is no slack, so each person tugging leaves the other uncovered.

The exception: on a frame with a footboard, such as a sleigh bed, the footboard stops the duvet sliding off the end, which is a genuine advantage of that style.

What tog you actually need

Thirteen and a half tog is a convention from draughtier housing. Modern UK homes are better insulated and more consistently heated, and 13.5 is the single commonest cause of overheating in bed.

If you had to own one duvet, 10.5 tog is the most useful. If you can own two, a 4.5 and a 9 combine to roughly 13.5 in the coldest weeks and separate for the rest of the year, which is what an all-seasons duvet is.

Tog measures thermal resistance, not weight or quality. A light high fill power down duvet and a heavy synthetic one at the same tog are equally warm, and the down one will feel less oppressive.

Two single duvets, which solves more than any mattress

Common across Scandinavia and worth considering seriously: each person has their own single duvet on a shared bed.

It resolves several complaints at once. Different temperature preferences, which is the most common disagreement in a shared bed and one no mattress can fix. Duvet stealing, which stops existing. And movement, because one person turning over no longer drags the covers.

It works properly from king width upward, where each person has 75 centimetres or more. At double width, with 67.5 centimetres each, two singles leave a visible gap down the middle.

The trade is that the bed looks less tidy, and you need two covers.

Covers, and the mistake that undoes good sizing

Buy the cover to match the duvet, not the bed. This is where people undo the one-size-up rule: they buy a king duvet for a double bed and then a double cover, which will not close.

A cover much larger than the duvet is also wrong, because the duvet bunches inside it and slides to one end.

Two features worth having: buttons hold better than poppers over years, and internal corner ties are the thing that actually stops a duvet migrating.

Washing, and the size that will not fit your machine

A king or super king duvet frequently will not fit a domestic washing machine, which means in practice it does not get washed.

That matters because allergen accumulates in the fill rather than the cover. If anyone in the house has a dust mite allergy, bedding needs washing at 60 degrees, since mites survive a 40 degree wash.

Two practical answers. An all-seasons duvet separates into two halves, each of which fits a domestic drum. Or a washable coverless duvet, which goes in whole.

Check the drum capacity against the duvet before buying, not after.

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