Find the label on the duvet
A cover marked king may not suit every duvet described with the same word. Start with the dimensions on the duvet's label or original product information. If those are unavailable, lay it out carefully and measure, allowing for its soft construction rather than stretching it to force a preferred number.
Then compare the cover's stated fit dimensions. Retailers may describe the size of duvet a cover is intended to fit rather than a casual measurement of the empty cover. Read the wording and ask when it is unclear.
As an example of a UK range, John Lewis lists standard duvet sizes including 135 by 200 cm for single, 200 by 200 cm for double, 230 by 220 cm for king and 260 by 220 cm for super king. Use those as a reference for that chart, not as proof that every imported product follows the same labels.
Keep mattress and duvet measurements separate
A mattress size helps with sheets, but it does not determine every duvet choice. Some people deliberately use a larger duvet for more coverage. If that is your arrangement, buy the cover for the duvet rather than automatically matching the mattress label.
Check orientation where the duvet is not square. A king duvet turned the wrong way can appear to fit poorly even when the dimensions are compatible. Labelled corners or the manufacturer's fastening arrangement may help identify the intended direction.
Look at the closure too. Buttons, poppers and ties differ in use, and the cover should be easy to secure without leaving the duvet bunched at one end.
Check the rest of the set separately
A bedding photograph may include pillowcases, sheets and decorative cushions that are not all sold together. Read the pack contents and compare pillowcase sizes with the pillows you own. A border can increase the outside dimensions without changing the size of pillow it fits.
Follow the product's care instructions rather than buying an incompatible size in the hope that washing will shrink it into place. Any stated shrinkage allowance belongs to the manufacturer's design, not an invitation to alter the fit with a hotter cycle.
Keep the duvet dimensions with your household notes. The next purchase then becomes a straightforward comparison of centimetres and pack contents, leaving colour and pattern as the enjoyable part of the choice.
