The bedding industry doesn’t follow standardized sizes—the dimensions of a king-size comforter and king-size duvet cover will usually vary by a few inches from brand to brand. In 2016 I tested each duvet cover with a Macy’s Hotel Collection Primaloft comforter that measured 96 inches by 101 inches, and in 2018 we used our former budget pick, the Pacific Coast European Down, which measured 98 inches by 108 inches (both are now discontinued). All of the king-size duvet covers I’ve tried fit these king-size duvets, and filled them out well when I made the bed. However, as an active sleeper, I sometimes noticed the duvet pulling away from the sides inside its cover, even when using corner ties. A larger, fluffier duvet helped curb a lot of this movement in our 2018 testing. It’s not a perfect solution, but if you tend to get tangled in your duvet cover with no duvet in sight, try looking for a cover that’s slightly smaller than your comforter, so there’s less chance it will shift inside.
