The standard size double bed is 54 inches by 75 inches. The Better Sleep Council recommends double beds for use by only one person, as they are short and can only accommodate someone who is 5 feet 5 inches or shorter.
A queen mattress, which is 60 inches by 80 inches, is larger than a double mattress. This gives 30 inches of personal space for two people. A king mattress, which measures 76 inches by 80 inches, provides each person 38 inches of personal space. This is equivalent to one twin mattress each. It may too big for some bedrooms and The Better Sleep Council recommends measuring the space before making a purchase.