A double size bunk bed can fit in a mattress the size of 54 x 75 inches, which is enough to comfortably accommodate a grown person (if that person is not extraordinary tall). Typically, double size bunk beds are used by kids who have out-grown their twin beds; teenagers, mostly, or perhaps an odd tween pre-destined to become a basketball player. Young adults living in space challenged quarters love them too.
Double over double bunk beds in particular are suitable wherever lots of sleeping space is needed, especially if living quarters are small. Families with multiple children love them, since such a bed can easily take in two smaller kids. A double/double bunk bed is also a practical solution for guest rooms; it will accommodate an entire mid-sized family, particularly if equipped with a trundle bed.
You’ll notice most of the products from the selection below are actually labeled as full size beds, but not to worry: full size, when it comes to mattress dimensions, is exactly the same as double size, it’s just that ‘full’ is a more common expression in the USA so most manufacturers are sticking with that.