Twin, 39" x 75"
Most often used in children's rooms and guest bedrooms. Also used for daybeds, trundle units, and hideaways. It's a narrow bed that's easy to make and can fit almost anywhere. Width per person: 39 inches.
Twin XL, 39" x 80"
Generally used in college dorm rooms, 5" longer than a standard twin. Limited bedding options. Width per person: 39 inches.
Full (Double), 54" x 75"
A good option for a guest room or as a child's step-up mattress. 15" wider than a twin bed, but only 75" long which may be too short for some adults. Not much room for 2 adults (each will have only 27" of width vs. 39" in a twin bed). Width per person: 54 inches (or 27 inches each).
Full XL, 54" x 80"
Good for one person sleep or a guest room, 5" longer than a full bed. Limited bedding options. Width per person: 54 inches (or 27 inches each).
Queen, 60" x 80"
Most popular bed size in the US, a good choice for guest rooms and smaller master bedrooms, 6" wider and 5" longer than a full bed. Each adult has 9" less than the width of a standard twin bed. Width per person: 30 inches each.
King (Eastern King), 76" x 80"
Good for two-person sleep, 16" wider than a queen bed. The eastern king is the only bed to give each person the same width as a twin bed. In fact, you can push 2 extra-long twin beds together to be the same size as an eastern king. This is a good way to have a versatile guest room (use 2 twins separately or push together to make a king bed for couples). Comes with two half-width box springs to be more manageable when moving. Width per person: 38 inches each.
California King (Western King), 72" x 84"
A better choice for taller adults, 12" wider and 4" longer than a queen bed. Bedding may be labeled either "California King" or "Western King". Comes with two half-width box springs to be more manageable when moving. Width per person: 36 inches each.