Murphy Bed Dimensions are twin Murphy bed is 39 inches wide by 75 inches long, twin extra long Murphy bed is 39 inches wide by 80 inches long, three quarter Murphy bed is 48 inches wide by 75 inches long, full Murphy bed or double Murphy bed is 54 inches wide and 75 inches long, full extra long Murphy beds are 54 inches wide by 75 inches long, queen Murphy beds are 60 inches wide by 80 inches long and king Murphy beds are 78 inches wide and 80 inches long. Murphy Size Mattress depths can vary from just a few inches to 14" or more, but because of the size and weight constraints, thinner is usually better. Many times, actual Murphy Bed mattress dimensions will vary by one or two inches, usually smaller. It is my understanding that the Murphy Bed is a generic term for a bed that hides inside of a wall or cabinet. This being the case, there are many manufacturers that build custom Murphy Beds with custom Murphy Bed mattresses so sizes can be all over the map.