Although a king-size duvet cover is slightly larger than the proportions of a queen-size bed, a king-size duvet cover can be used on a queen-size bed. A duvet cover fits over a duvet or comforter, which is sold according to mattress size.
The dimensions of a queen-size mattress are 60 by 80 inches. The dimensions of a standard king-size mattress are 76 by 80 inches; a California king mattress is slightly shorter and longer, measuring 72 by 84 inches. For an optimal fit, purchase a duvet and duvet cover in the same size as that of the mattress. If the duvet and duvet cover are larger than the mattress, the duvet may appear too wide for the bed.