A twin bed is the smallest adult mattress size, and it measuresÂ approximately 38 inches wide by 75 inches long. Twin beds and full size beds are actually both the same length. For individuals who are tall but require a twin sized bed, a twin extra-long mattress size is available.
The extra-long twin mattress can actually be found in most college dormitories. It is 5-inches longer than a standard twin bed, and it is the same length as a king or queen-sized mattress.
A twin bed is made to suit a child or one adult. Twin mattresses are commonly found in daybeds and bunkbeds. The only mattress smaller than a twin is a crib size.