The image above is a lifesize model of a Great Hammerhead Shark, the average size of which is about 11 feet in length. The largest member of this species reported, was 20 feet long. These sharks average about 500 pounds, but can weigh up to 1,000 pounds. Many species of hammerheads are harmless to humans, but a few species, like the great hammerhead, can be very dangerous.