What are the standard dimensions of a king mattress?

A standard king mattress measures 76 inches wide by approximately 80 inches long. The width and length of a king bed are about the same as can be achieved by pushing two extra long twin beds together.

King mattresses are popular options for couples, since they afford plenty of personal sleeping space for two without crowding. However, their large size can make for a tight fit in small rooms. At about 18 inches wider than queen mattresses, king mattresses can also be difficult to negotiate around corners or through hallways or haul up steep flights of stairs. California king mattresses are 4 inches longer yet 4 inches narrower than a regular king.