A full-sized mattress is 54 inches wide, according to Bedding Experts retailers. This is the equivalent width of two crib mattresses. Though two people can sleep on a full-sized mattress, greater comfort is achieved with a queen-sized mattress.
The standard full-sized mattress is 75 inches long. Extra-long full-sized mattresses can often be special-ordered, claims Bedding Experts retailers. A queen-sized mattress gives 6 inches of extra width and 5 inches of extra length, as opposed to the standard full-sized mattress, and is often purchased to sleep two adults. The standard twin mattress is the same length as the standard full-sized mattress but is only 39 inches wide.