The difference between a full-size and a king-size bed is one of size, with full-size mattresses being 53 inches wide and approximately 75 inches in length. A king-size mattress is 76 inches wide and 80 inches long.
A full-size mattress provides only enough space for a single person to sleep under most circumstances, and is a popular choice for younger children and teenagers. King-sized mattresses, on the other hand, are recommended for couples who want a maximum amount of personal sleeping space. The problem with this size bed, however, is that due to its oversized bulk, placing them in smaller bedrooms may be difficult.