A queen-size mattress is 60 inches wide and 80 inches long. The queen-size mattress is six inches wider and five inches longer than a double mattress, and 21 inches wider and five inches longer than a twin-size mattress.
Double mattresses, at 54 inches wide and 75 inches long, were the most common size for accommodating two people until the 1960s. They provide about 27 inches of space per person, while a queen-size mattress provides about 30 inches of space. By contrast, a king-size mattress is 76 inches wide and 80 inches long, meaning that it provides 38 inches of space per person. A California king-size mattress is longer, at 84 inches, but narrower, at 72 inches.