A split king mattress is two mattresses placed on top of a box spring to make one king-size bed. These types of mattresses are ideal for people who want some extra sleeping room but can't fit a single king-size mattress in a bedroom because of a narrow hallway or staircase.
Each individual mattress for a split king-size bed is 38-by-80 inches. A regular king-size mattress measures 76-by-80 inches so you're not losing any sleeping room. The mattresses are placed on a king-size box spring or on a split king box spring. The depth of the mattresses will vary, depending on the brand name.
Split King Sheets
There is a split king-size sheet set or a regular king-size sheet set. The split king sheet set has two fitted sheets, one measuring 38-by-80 inches with pockets deep enough to fit mattresses 18 inches deep. The other flat sheet is 110-by-104 inches. The set includes two king-size pillow cases measuring 21-by-42 inches.
Although there are split king sheet sets, the regular king-size bedsheets will fit a split king mattress and cover both mattresses with one sheet, making the bed look as if it has one mattress, not two. King-size fitted sheets measure 78-by-80 inches, the flat sheet is 110-by-102 inches and the pillow cases are 20-by-40. Most fitted sheets come with 18-inch-deep pockets, but some may be 16 inches deep. You need to look for a set with a deep pocket if your mattresses have depths of more than 15 inches.
Besides being easier to navigate sharp corners and narrow staircases, the split king mattress is ideal for people who don't have a lot of room for an extra bed for company. With the split king-size mattress, you could lay one mattress on the floor for company and have two bed mattresses. But you would need the split king bedsheets to separate the mattresses.