The king and California king mattress sizes are the largest standard sizes available. Consumers who want to purchase a larger bed must have one custom made. Some companies developed programs for extra-large mattresses, such as Selectabed.com, which produces "Ultra King Size" mattresses of varying dimensions.
A king size mattress is 76 inches wide and 80 inches long. The California king takes up the same amount of space, but is longer and narrower to accommodate taller sleepers. However, even a California king might not offer sufficient height for extremely tall people, in which case a custom mattress size might be required.