The largest turtle to ever live is the archelon, which measured 15 feet long and weighed almost 5000 lbs. The largest turtle that still exists today is the leatherback sea turtle, which is around half the size at 7 feet long and just over 2000 lbs in weight. In addition to being the largest living turtle, the leatherback is also the fastest non-avian reptile and the largest reptile that isn’t a crocodile in the world.