We have a twin xl mattress that our son used for 3 months while in college. It is in very good shape. A twin XL mattress is 38 inches wide by 80 inches long, making it the same width as a twin mattress but 6 inches longer. This extra length provides more legroom and is a good option for taller people or rooms with limited space. Twin XL mattresses are also a popular choice for college dorms or apartments.