The mattress for a full bed is 54 by 75 inches, which is the same length as a twin bed but 15 inches wider. A twin bed gives a sleeper the minimum required sleeping space. A full bed provides an individual a more comfortable sleeping space, as described by Sleepy's.
Twin beds are often a good choice for younger children and for rooms in which there is not much space, notes Sleepy's. Older children and teens sometimes graduate to full beds.
The height of mattresses varies from 9 to 16 inches, depending on the type of mattress, not the size. Pillow-top mattresses can be 15 to 16 inches high. Box springs and frames also increase the height, according to About.com.