Standard king and California king mattress have different widths and lengths. A standard king-size mattress measures 76 inches wide and 80 inches long, while a California king measures 72 inches in width and 84 inches in length.
The standard king mattress, sometimes referred to as an Eastern King, is the widest mattress available at a full four inches wider than the California king. While the 80-inch length provides plenty of legroom for most people, the four extra inches in width sometimes makes it more difficult to place in smaller rooms. The California King, while longer, is sometimes not wide enough for two adults to sleep comfortably.