Queen size comforters fit a mattress and box spring that are 60 inches across by 80 inches in length. They are generally 86 inches wide by 94 inches long.
King size comforters fit a mattress and box spring that are 78 inches across by 80 inches in length. They are about 96 inches across by 110 inches in length.
A deep pillow-top mattress will require a comforter on the larger end of the range to allow for a longer drape over the sides of the mattress.
A fluffier comforter will require a few extra inches to account for the loft of the filling. A queen or full size down comforter is about 90 by 98 inches, while a king down comforter measures about 98 by 108 inches.
Bed Skirt Significance
Comforters drape a few inches below the top mattress, while a bed skirt covers the box spring. To avoid the need for a bed skirt on the box spring, choose a bedspread that reaches the floor.