The female wedge-tailed eagle weighs between 3.0 and 5.8 kg (6.6 and 12.8 lb), while the smaller males weigh 2 to 4 kg (4.4 to 8.8 lb). Length varies between 81 and 106 cm (32 and 42 in) and the wingspan typically is between 182 and 232 cm (6 ft 0 in and 7 ft 7 in). In 1930, the average weight and wingspans of 43 birds were 3.4 kg (7.5 lb) and 204.3 cm (6 ft 8 in). The same average figures for a survey of 126 eagles in 1932 were 3.63 kg (8.0 lb) and 226 cm (7 ft 5 in), respectively. The largest wingspan ever verified for an eagle was for this species. A female killed in Tasmania in 1931 had a wingspan of 284 cm (9 ft 4 in), and another female measured barely smaller at 279 cm (9 ft 2 in). Similar claims, however, have been made for the Steller’s sea eagle, which has also been said to reach or exceed 2.74 m (9 ft) in wingspan. Reported claims of eagles spanning 312 cm (10 ft 3 in) and 340 cm (11 ft 2 in) were deemed to be unreliable. This eagle’s great length and wingspan place it among the largest eagles in the world, but its wings, at more than 65 cm (26 in), and tail, at 45 cm (18 in), are both unusually elongated for its body weight, and eight or nine other eagle species regularly outweigh it.
Young eagles are a mid-brown colour with slightly lighter and reddish-brown wings and head. As they grow older, their colour becomes darker, reaching a dark blackish-brown shade after about 10 years (birds in Tasmania are usually darker than those on the mainland). Adult females tend to be slightly paler than males. Although it rarely needs to be distinguished from other Aquila eagles, its long, wedge-shaped tail is unique to this species.
Its range and habitat sometimes overlap with the white-bellied sea eagle, which is similar in size and shape, and also has a somewhat wedge-shaped tail, although rather smaller and less distinctive. In silhouette and poor light, the two can look somewhat similar. Closer examination reveals the belly colour or tail size to distinguish the two.