The typical king size duvet is approximately 108 inches by 94 inches. However, because king size beds vary in size, the matching duvets also show a fair amount of variation in size. King size duvets can range from 102 inches to 114 inches running vertically along the length of the bed and from 86 inches to 102 inches running along the foot of the bed.
American king size beds come in two basic sizes. The standard king size bed, sometimes known as the Eastern king, is 76 inches wide by 80 inches long. The California king size bed is narrower but longer, at 72 inches wide and 84 inches long. A typical duvet of 104 inches by 88 inches can be used to cover either size since the duvet is designed and cut to hang over at least three sides of the bed. To make one of these duvets, 6 to 9 yards of fabric is required.
In Europe, mattress sizes are different as are duvets and duvet covers. What is considered a king size bed in Europe is, at 59 inches by 78 inches, just a bit smaller than an American queen size bed. A standard European king size duvet, at 86 inches by 90 inches, would therefore not come close to covering an American king size bed adequately. The closest European equivalent to the American king size bed is known as the emperor size mattress and requires a duvet measuring approximately 92 inches by 114 inches.