Duvet Size Calculator

What size duvet do you actually need?

A duvet that only just covers the top of the mattress always feels too small, because a duvet has to do two jobs at once: cover the sleeping surface and drape over the sides far enough to stay put through the night. The standard rule is simple. Take the width of your mattress, add the drape you want on each side, and that total is your ideal duvet width. For length, add one drape allowance at the foot end, since the top end tucks under the pillows. A 140 centimetre double mattress with a 30 centimetre drape on each side therefore needs a duvet about 200 centimetres wide and 230 centimetres long. That is why shop sizes often look much bigger than the bed they are sold for, and why buying a duvet the same width as your mattress leaves you cold at the edges.

Drape is a matter of taste as much as measurement. A short drape of 20 to 25 centimetres per side gives a neat, tailored look and works well in small bedrooms where a long overhang would brush the floor or bunch against bedside tables. A generous drape of 35 to 45 centimetres looks luxurious, hides an unattractive bed base, and gives couples more cover to share without fighting over the middle. The trade-off is weight and bulk: a bigger duvet is heavier to shake out, slower to dry, and needs a larger cover. If two people share the bed, err on the generous side, because a duvet that is only just wide enough will always migrate to one side overnight.

Standard duvet sizes and what they fit

Manufacturers do not all use identical measurements, but the common sizes are stable enough to shop with confidence. A single duvet is usually around 135 by 200 centimetres and suits a standard single bed of 90 by 190 centimetres with a modest drape. A double is typically 200 by 200 centimetres, which gives a generous drape on a 135 or 140 centimetre mattress. A king is usually 225 by 220 centimetres and fits 150 to 180 centimetre beds, while a super king at around 260 by 220 centimetres suits 180 centimetre beds and anyone who wants maximum overhang. Always check the label rather than trusting the name alone, because one brand's king can be another brand's queen, especially with imported bedding.

How to measure your bed properly

Measure the mattress itself, not the bed frame, because frames can be wider than the mattress and will mislead you. Measure width across the widest point, including any pillow-top bulge, and measure length from head to foot along the top surface. If your mattress is deep, say 30 centimetres or more, remember that the drape has to clear that depth before it hangs freely, so a deep mattress eats into your effective overhang. In that case add 5 to 10 centimetres to your drape target. Also check the height of the bed base: a duvet that hangs to the floor looks lovely in a showroom but collects dust and trips the dog in a real bedroom, so leave at least a few centimetres of clearance.

Duvet length: the forgotten measurement

Most people obsess over width and ignore length, yet length is what keeps your feet covered. A duvet should extend at least 20 to 30 centimetres beyond the foot of the mattress so it can be tucked or left to fall naturally without pulling up during the night. Tall sleepers should add extra length rather than extra width, and look for duvets labelled extra long, which are usually 220 to 230 centimetres instead of 200. If you sleep with the duvet tucked under your feet, add another 10 centimetres. A duvet that ends exactly at the mattress foot will ride up every time you bend your knees, and no amount of width fixes that.

Sharing a bed: one duvet or two?

Couples face a choice that sizing alone cannot solve. One large duvet looks tidy and feels romantic, but it guarantees nightly negotiation, because the person who moves most tends to steal the most cover. The Scandinavian sleep method solves this by giving each sleeper their own single or small double duvet, sized to their half of the bed plus a drape on the outer side only. On a 180 centimetre super king, two 140 centimetre duvets give each person generous coverage with no tug of war. It looks unusual at first, but hotels across Scandinavia use it for a reason, and many couples who try it never go back to sharing.

Tog, fill, and why size affects warmth

A bigger duvet is not automatically warmer, but size and warmth interact in ways worth knowing. A duvet that drapes well down the sides seals in warm air and stops draughts sneaking in at the edges, which matters more than a small change in tog rating. Conversely, an oversized duvet folded double across the bed traps extra air and feels warmer, which is useful in winter but stifling in summer. Fill type also matters: down and feather drape softly and follow the body, while hollowfibre holds its shape and can feel stiffer at the edges. If you sleep hot, choose the smaller end of your size range and a lower tog, and let the drape do the insulating work.

Common sizing mistakes to avoid

The most common mistake is buying the duvet size that matches the bed name rather than the mattress measurement. A double bed can be 135 or 140 centimetres wide, and a king can be 150 or 180, so the name alone is not enough. The second mistake is forgetting the cover: a duvet and its cover must match, and a cover that is 10 centimetres too small will bunch the filling and create cold, flat patches. The third mistake is sizing for the bed you have today when a new mattress is coming, since a deeper replacement mattress changes the effective drape. Measure twice, check the label dimensions in centimetres, and keep the receipt until you have tried the duvet on the bed for a night.

Duvet covers, protectors, and washing

Your duvet size decision also decides your cover size, protector size, and laundry logistics. A super king duvet needs a super king cover, which is a large item to wash and may not fit a small domestic machine comfortably. If you use a laundrette, check that its machines take your size before committing to the largest option. A protector adds a centimetre or two of bulk but saves the duvet from spills and allergens, and it is far cheaper to replace than the duvet itself. When in doubt between two sizes, choose the larger one for the bed and accept the extra laundry, because a duvet that is too small cannot be fixed, while a slightly large one can always be folded.

Small bedrooms and low beds

In a small room, a very generous drape can make the bed look enormous and crowd the walkways on either side. If you have less than 50 centimetres of clearance beside the bed, choose a drape of 20 to 25 centimetres so the duvet does not brush furniture or the floor. Low platform beds also suit a shorter drape, since there is less base to hide and a long overhang will pool on the floor. The calculator above lets you test drape values before buying, so try your room's real clearances rather than guessing from a showroom display.

Seasonal sizing: one duvet or two weights?

Many households keep one duvet size year round and change only the tog, which is sensible because it means one set of covers. Others use a lighter, slightly smaller duvet in summer, since less drape means less trapped heat. If you go that route, keep the summer duvet no more than one size smaller, or the change in look will be obvious and the bed will feel underdressed. An all-season duvet, usually two thinner duvets that clip together, gives you both weights in one size, which is the tidiest solution for anyone short on storage space.

• Measure the mattress, not the frame, in centimetres.
• Add your chosen drape to each side for width, and once at the foot for length.
• Deep mattresses need 5 to 10 centimetres of extra drape.
• Check label dimensions, not just the size name.
• Match the cover exactly to the duvet you buy.

Getting duvet size right is a small decision that pays off every single night. A duvet that drapes properly stays in place, seals out draughts, and makes the whole bed look finished, while one that is too small is a nightly annoyance no tog rating can fix. Measure your mattress, pick a drape that suits your room and your sleeping habits, and use the calculator above to turn those two numbers into a size you can shop for with confidence.