Twin Xtra Long is 38 inches wide by 80 inches long
Queen is 60 inches wide by 80 inches long
King (one piece) is 76 inches wide by 80 inches long
King split (2 Twin Xtra Long) is 76 inches wide by 80 inches long. This is the most popular king since each sleeper has their own controls to adjust their bed for personal comfort.

Please keep in mind that an adjustable bed and mattress measurement can vary a fraction of an inch.