Homarus americanus commonly reaches 8–24 inches (200–610 mm) long and weighs 1–9 pounds (0.45–4.08 kg) in weight, but has been known to weigh as much as 44 lb (20 kg), making this the heaviest crustacean in the world.
Together with Sagmariasus verreauxi, it is also the longest decapod crustacean in the world; an average adult is about 9 in (230 mm) long and weighs 1.5 to 2 lb (680 to 910 g).
The longest American lobsters have a body (excluding claws) 64 cm (25 in) long.
According to Guinness World Records, the heaviest crustacean ever recorded was an American lobster caught off Nova Scotia, Canada, weighing 44.4 lb (20.1 kg).

The closest relative of H. americanus is the European lobster, Homarus gammarus.
The two species are very similar, and can be crossed artificially, although hybrids are unlikely to occur in the wild since their ranges do not overlap.
The two species can be distinguished by several characteristics:
The rostrum of H. americanus bears one or more spines on the underside, which are lacking in H. gammarus.

The spines on the claws of H. americanus are red or red-tipped, while those of H. gammarus are white or white-tipped.

The underside of the claw of H. americanus is orange or red, while that of H. gammarus is creamy white or very pale red.
Homarus americanus commonly reaches 8–24 inches (200–610 mm) long and weighs 1–9 pounds (0.45–4.08 kg) in weight, but has been known to weigh as much as 44 lb (20 kg), making this the heaviest crustacean in the world. Together with Sagmariasus verreauxi, it is also the longest decapod crustacean in the world; an average adult is about 9 in (230 mm) long and weighs 1.5 to 2 lb (680 to 910 g). The longest American lobsters have a body (excluding claws) 64 cm (25 in) long. According to Guinness World Records, the heaviest crustacean ever recorded was an American lobster caught off Nova Scotia, Canada, weighing 44.4 lb (20.1 kg).
The closest relative of H. americanus is the European lobster, Homarus gammarus. The two species are very similar, and can be crossed artificially, although hybrids are unlikely to occur in the wild since their ranges do not overlap. The two species can be distinguished by several characteristics:
The rostrum of H. americanus bears one or more spines on the underside, which are lacking in H. gammarus.
The spines on the claws of H. americanus are red or red-tipped, while those of H. gammarus are white or white-tipped.
The underside of the claw of H. americanus is orange or red, while that of H. gammarus is creamy white or very pale red.
American lobster