The dimensions of a California King mattress are 72 inches wide by 83.5 inches long, according to a size chart provided by Serta. Many bedding charts list the California King mattress as 72 by 84 inches in length, including the Better Sleep Council and The Bedding Experts.
A California King mattress is 4 inches longer than a standard king mattress, but it is not as wide. A traditional king mattress is 76 inches in width, which is exactly the same width as two twin mattresses, according to Serta. The traditional king gives couples the most possible personal space, according to the Better Sleep Council.