Split king size mattresses, also known as “Split Eastern King” size mattresses are similar to king size mattresses, except the mattress is “Split” vertically down the middle, offering 2 separate mattresses & sleeping surfaces.  Split king size mattresses is an industry standard size with the dimensions of each split king mattress measuring 38” x 80” inches in length & width.  Best used as part of a dual-comfort sleep system, with each split king mattress being a different comfort i.e. left side firm, right side soft.