A full-size mattress, also known as a double mattress, measures 54 inches wide by 75 inches long. It provides enough space for one or two sleepers, making it a popular choice for guest rooms, smaller bedrooms, or for individuals who prefer more sleeping space than a twin mattress offers. This mattress size strikes a balance between comfort and space efficiency, fitting well in various room layouts. While it may not be as spacious as a queen mattress, it is often more affordable and easier to move, making it a practical option for many households.