A standard twin size mattress is 38 inches wide by 75 inches long, according to Consumer Reports. A twin mattress, sometimes called a single, is the smallest mattress size available beyond a crib mattress, as explained by The Better Sleep Council.
Some adults, men in particular, may find that a standard twin size mattress is too short for comfort. A twin extra-long (XL) mattress is also available. This mattress type is several inches longer than a regular twin mattress and is commonly used in college dorm rooms. It is especially recommended for small spaces, according to The Better Sleep Council.