I am making a king sized quilt for a relative who has a comforter that is 90" x 102", and she wants the quilt to be roughly the same size. The quilt I am making for her will end up approximately 90" long and 107" wide.
Her comforter hangs down far enough on each side to completely cover the box springs and reach the top of the wooden bed frame, and that's enough for her. She doesn't want it so long and heavy that it's hard to pull straight when she's in bed under it.