How Big Do Alligator Snapping Turtles Get? Size Records

Typical adult size

The alligator snapping turtle becomes able to breed at a shell (carapace) length of about 33 cm (13 in) and a weight of about 8 kg (18 lb). After that it keeps growing, slowly, for the rest of its life. That is why size varies so much between adults: a young breeding female and an old male can differ in weight by a factor of five or more.

Most adults found in field surveys are well below the famous giant sizes. Studies of wild populations that weighed dozens to hundreds of adults found average weights of roughly 13 to 21 kg (30 to 46 lb). Turtles heavier than about 45 kg (100 lb) do occur, but in most studies they are rare and almost always old males.

Males vs females

Male alligator snappers grow much larger than females. In a long-term study in the Suwannee River, where the closely related Suwannee alligator snapping turtle lives, adult males averaged about 38 kg (84 lb) and females about 17 kg (37 lb). The same pattern holds for Macrochelys temminckii: the giants in museum and aquarium records are almost all males.

Males can also be told apart by a thicker tail base and by the position of the vent, which lies beyond the rear edge of the shell in males but at or inside the edge in females.

Record sizes: verified and disputed

The heaviest reliably weighed alligator snapping turtles lived in captivity, where they had steady food and no risk of being harvested:

• A turtle kept for 16 years at the Shedd Aquarium in Chicago weighed about 113 kg (249 lb) before it was moved to the Tennessee Aquarium on a breeding loan in 1999.
• A turtle at the Brookfield Zoo near Chicago weighed about 107 kg (236 lb).
• A turtle of about 135 kg (298 lb) has also been reported, but the details are less well documented.

The most famous figure, a 183 kg (403 lb) turtle supposedly found in Kansas in 1937, has never been verified and should be treated as a story rather than a record. Claims of wild turtles over 100 kg (220 lb) appear regularly on social media, but weights given without a scale or a scientific report are usually estimates and often exaggerated.

How fast do they grow?

Alligator snapping turtles grow slowly. They reach maturity at about 11 to 13 years of age, and growth continues for decades afterward at a decreasing rate. A turtle of more than 45 kg (100 lb) is therefore usually several decades old.

This slow growth matters for conservation. When big adults were harvested heavily for meat in the 20th century, populations lost exactly the animals that produce the most eggs, and it takes many years for replacements to grow up. Today the species is listed as Endangered on the IUCN Red List.

Captive turtles can grow larger and heavier than most wild ones because they are fed regularly, so record weights from zoos and aquariums are not typical of wild adults.

How do they compare with other turtles?

Among living freshwater turtles, only a few Asian giant softshell turtles of the genera Chitra, Rafetus and Pelochelys reach a comparable size. In North America, nothing else comes close. The common snapping turtle, the next-biggest snapper, usually weighs 4.5 to 16 kg (10 to 35 lb), and the heaviest wild one reported weighed about 34 kg (75 lb). The differences are laid out in alligator snapping turtle vs common snapping turtle.

Sea turtles are a different story. The leatherback sea turtle, the largest living turtle, usually weighs 250 to 700 kg (550 to 1,540 lb), several times more than any alligator snapper.

Why is the head so big?

Much of an alligator snapper’s bulk is in its head and jaws. The head is wide and heavy, with a sharply hooked beak, and bite force rises steeply with body size: a 2023 study found that small turtles bite weakly, while the largest ones tested produced forces of nearly 1,900 newtons. A big head suits an ambush hunter that must grab and hold slippery fish, other turtles and hard-shelled mussels.

Can you judge size from a photo?

Often not. Alligator snappers are usually photographed close up, and their huge heads make them look even bigger than they are. Reliable records come from turtles weighed on a scale and measured along the straight length of the shell. If you see a large turtle in the wild, admire it from a safe distance and do not try to lift it: big snappers are heavy and can bite hard.