All waterbed measurements, including those of the California king, use only the actual sleeping space of the bed, not including the frame. This means that the dimensions of a California king waterbed are taken from the interior edge of one side of the frame to the interior edge of the other side of the frame, and from the interior edge of the head of the frame to the interior edge of the foot of the frame.
The Dimensions of the California King
A California king waterbed, sometimes just referred to as a king waterbed, is the same size as a California king mattress made for a traditional bed. The length of the California king waterbed mattress, or sleeping space inside of the waterbed frame, is 84 inches.
The width of the California king waterbed mattress is 72 inches across.
Other Waterbed Sizes
All waterbed mattresses and frames, from the smallest super-single frame to the California king, are the same 84-inches in length. The mattresses do, however, vary in width.
The next largest waterbed size after the king, the queen-size waterbed, measures 60 inches in width, while the super-single waterbed measures 48 inches in width. ABC Waterbed recommends the super-single waterbed for single sleepers and both the queen and king sizes for two adults.
Dressing the Bed
Since waterbeds differ in size from traditional bed frames and mattresses, you cannot generally fit a standard sheet set onto the waterbed. You can get properly-fitted sheets for a California king waterbed by purchasing waterbed sheet sets in that size.
Waterbed sheet sets are specially designed to fit the thick mattress and also to cling to the slick surface of the mattress more effectively than standard sheet sets.