Steller's Sea-eagle is the biggest bird in the genus Haliaeetus and is one of the largest raptors overall. Females typically weigh from 6.8 to 9 kilograms (15 to 20 lbs), while males are rather lighter with a weight range from 4.9 to 6 kilograms (11 to 13 lbs). At its average weight, the Steller's outweighs both the average Harpy and the average Philippine Eagles by over 0.5 kilograms (1.1 lb). An unverified record exists of a huge female, who apparently gorged on salmon, having weighed 12.7 kilograms (28 lbs). The Steller's Sea Eagle's length can range from 85 to 105 cm (33 to 41 in). The wingspan is from 1.95 to 2.5 m (6.4 to 8.2 ft) and each wing chord is 57–62 cm (22–24 in).
The Steller's sea eagle has the second largest median wingspan of any eagle. Both the wing chord and wingspan, at an average of 2.13 m (7.0 ft), are similar or slightly smaller than to those of the Steller's close relative the White-tailed Eagle (Haliaeetus albicilla) The Steller's Sea-eagle mainly feeds on fish. Favored prey include salmon , trout and cod. Like most Haliaeetus eagles, they hunt fish almost exclusively in shallow water. Relatively large numbers of these normally solitary birds can be seen congregating on particularly productive spawning rivers due to an abundant food supply. Besides fish, it also regularly preys on water-dwelling birds, including ducks, geese, swans, cranes, herons and gulls. After courtship, which usually occurs between February and March, the animals lay their first white-green eggs around April to May. Usually only one chick survives.