The full size mattress, also known as a double mattress, is approximately 16 inches wider than a twin mattress, but does not provide enough added room for two people to sleep comfortably. It may be too short for adults taller than 5’5”. Full beds are 54 inches wide by 74 inches tall. A full size mattress is a great choice for growing children, plus the added space allows for parents to lie down while tucking their kids in for the night.