Full-size mattresses are 75 inches long and 53 inches wide. They are approximately 15 inches wider than a twin-size mattress. This size is suited for single sleepers. Sharing it with someone will only leave about 27 inches of personal space. The length of this mattress may be too short for some adults. While adults can use them, a full-size mattress is best for teenagers and younger children. Kids will have a lot of room sleeping in this mattress size, and it will take longer for them to outgrow it.