A double or full-size mattress is about 53 inches wide and 75 inches long. If two people share a double mattress, each individual has a space about 27 inches wide, which is about the same width as a crib mattress.
The Better Sleep Council recommends double mattresses only for single sleepers who are 5-feet-5-inches tall or shorter. A queen-size mattress is 60 inches wide and 80 inches long, large enough for many couples. The queen-size mattress is an appropriate size for guest rooms and small master bedrooms, according to the council. King-size mattresses are 76 inches wide and 80 inches long, and this size is often too big for tight stairways or narrow hallways.