King size mattresses, also referred to on the West Coast as Eastern King mattresses, are 76 inches wide and 80 inches long.
California King mattresses are 72 inches wide and 84 inches long. They are 4 inches narrower and 4 inches taller than regular king size beds. Therefore, mattress pads will need to be sized and fitted accordingly.
Mattress pad pockets range in depth from 14 inches up to 22 inches. Standard size for most mattresses is 14-20 inches, regardless of the mattress' size. Pillowtop mattresses and many new modern mattress styles require a deep pocket. Be sure to measure the height of your mattress before purchasing a mattress pad for your California King or King mattress.