How Big Do Lobsters Get? The Largest Lobster on Record

How big is a typical lobster?

An average adult American lobster is about 23 cm (9 in) long from the tip of its head to the end of its tail and weighs about 0.7–0.9 kg (1.5–2 lb). Lobsters sold for food are usually smaller still, often 0.5–1 kg (1–2 lb), because most are caught within a few years of reaching the minimum legal size.

Scientists and fishery officers measure lobsters by carapace length: the distance from the eye socket to the back of the body shell. In most United States waters, the legal minimum carapace length is about 83 mm (3.25 in). Maine also sets a maximum of 127 mm (5 in), so the biggest lobsters there must be returned to the sea.

The largest lobster ever recorded

The heaviest lobster on record was caught off Nova Scotia, Canada, in 1977. Guinness World Records lists it at about 20.1 kg (44.4 lb) and about 1.06 m (3 ft 6 in) from the end of the tail fan to the tip of the largest claw. No crab, shrimp or other crustacean has been reliably recorded at a greater weight.

Measured by body length alone, the longest American lobsters reach about 64 cm (25 in) without their claws, according to the FAO’s catalogue of the world’s marine lobsters.

Other giants make the news from time to time. In 2009, for example, a 9.1 kg (20 lb) lobster nicknamed George, caught off Newfoundland, was released from a New York restaurant after an animal-rights campaign. Lobsters of this size are rare, though, and most reports involve animals from deeper offshore waters.

How long does it take a lobster to grow that big?

Lobsters grow in steps, by molting their hard shell and building a bigger one. Young lobsters molt about ten times in their first year and reach only 2.5–3.8 cm (1–1.5 in) long. They then molt about 20–25 times over 5–8 years before reaching roughly 0.45 kg (1 lb).

Each molt can add 40–50% to a lobster’s weight, but molts become rarer with age: about once a year for young adults and only every few years for large ones. Growth also depends on water temperature, since lobsters in warmer water molt more often than those in cold northern seas.

This means the true giants are almost certainly old, perhaps many decades old. Exactly how old is unknown, because lobsters shed every hard part of their shell when they molt and leave no growth rings to count. The often-quoted ages of 100 years or more for record lobsters are guesses, as explained in do lobsters live forever?

How big are lobster claws?

The two claws are different. The crusher is heavy and blunt, with rounded knobs for cracking shells, while the cutter is slimmer and has sharp teeth for gripping and tearing. In adult males the claws grow faster than the rest of the body, so the biggest old males carry huge claws for their size. Females put more of their growth into a broader tail, where they carry their eggs.

Claws can also be lost in fights or to predators. A lobster can regrow a missing claw, but the new one starts small and takes several molts to catch up in size.

Where do the biggest lobsters live?

The largest American lobsters are found mainly offshore, along the outer edge of the continental shelf and near underwater canyons, at depths down to about 700 m (2,300 ft). Many of these big lobsters migrate toward shallower water in spring and back out in fall.

Near the coast, where fishing is intense, few lobsters survive long enough to become giants. That is one reason some areas protect large lobsters. Big females are especially valuable to the population: a female 18 cm (7 in) long lays about 3,000 eggs, while one 45 cm (18 in) long can lay about 75,000.

How do American lobsters compare with other lobsters?

The European lobster of the eastern Atlantic is the American lobster’s closest relative and has a similar shape, but it stays much lighter. Spiny lobsters, such as the Caribbean spiny lobster of Florida and the Caribbean, have no large claws. Instead they defend themselves with long, spiny antennae and can make a loud rasping sound by rubbing a part at the base of each antenna. The eastern rock lobster of Australia and New Zealand rivals the American lobster in length, but without heavy claws it comes nowhere near its weight.

Some crabs are larger in other ways. The Japanese spider crab has legs spanning up to about 3.7 m (12 ft), the widest of any arthropod, but its body is only about 40 cm (16 in) across, and it is lighter than the record lobster. To see how lobsters rank among ocean giants, visit the largest animals in the world, or compare body plans in crab vs lobster.