King sized comforters are generally 110 inches by 96 inches. This can vary from manufacturer to manufacturer; comforters labeled as "king-sized" may be slightly larger or smaller than the aforementioned dimensions.
King sized mattresses are some of the largest available, so comforters need to be even larger to be able to fully cover the bed and its occupants. When shopping for a king sized comforter, it is best to know your mattress dimensions and how you want the comforter to lay over the bed. Typically, comforters are larger than the length and width of the bed and are designed to hang over the sides when unoccupied.