Typically, twin beds are distinguished from twin XL beds by their length. Although the width is equal, twin XL beds are 5 inches longer than their regular twin counterparts.
Twin beds come in two different sizes: the regular twin, which measures 39 x 75 inches, and the twin XL, which measures 39 x 80 inches. The additional length on a twin XL mattress is, according to Sleepy's, the most common type of mattress found in college dorm rooms because it can accommodate a broader range of heights. Typically, twin beds are most often found in children's bedrooms. Twin XL mattresses are also called extended twins and can sleep an adult comfortably.