The adults have an average weight of 20–27 kg (44–60 lb) and often measure 127 to 140 cm (50 to 55 in) long from beak to tail; they usually stand about 1.5 m (4 ft 11 in) tall, with a typical range of 1.4 to 1.7 m (4 ft 7 in to 5 ft 7 in), to the top of the head.
The males are generally bigger than the females.
Despite the delineation of this species as the "greater rhea" versus the lesser rhea, some data on body masses indicates that both species average about 23 kg (51 lb) in weight, but even at mass parity that greater species appears larger and is taller due to its longer legs and neck, whereas the lesser rhea is more compact and more so resembles an outsized, long-necked turkey in build.
 Elsewhere, the lesser rhea has been cited with a lower average weight of 16 kg (35 lb).
In some areas, male greater rheas weights of up to 35 kg (77 lb) are not uncommon and even females of up to 30 kg (66 lb) have been weighed, both weights higher than the maximum known mass for the lesser rhea.
Large males can weigh up to 40 kg (88 lb), stand nearly 1.83 m (6.0 ft) tall and measure over 150 cm (59 in) long, although this is uncommon.

The head and bill are fairly small, the latter measuring 8–10.4 cm (3.1–4.1 in) in length.
The legs are long, with the tarsus measuring between 33.5 and 37 cm (13.2 and 14.6 in), and strong and have 22 horizontal plates on the front of the tarsus.
They have three toes, and the hind toe is absent.
The wings of the American rhea are rather long; the birds use them during running to maintain balance during tight turns, and also during courtship displays.

Greater rheas have a fluffy, tattered-looking plumage, that is gray or brown, with high individual variation, The head, neck, rump, and thighs are feathered.
In general, males are darker than females.
Even in the wild—particularly in Argentina—leucistic individuals (with white body plumage and blue eyes) as well as albinos occur.
Hatchling greater rheas are grey with dark lengthwise stripes.
The adults have an average weight of 20–27 kg (44–60 lb) and often measure 127 to 140 cm (50 to 55 in) long from beak to tail; they usually stand about 1.5 m (4 ft 11 in) tall, with a typical range of 1.4 to 1.7 m (4 ft 7 in to 5 ft 7 in), to the top of the head. The males are generally bigger than the females. Despite the delineation of this species as the "greater rhea" versus the lesser rhea, some data on body masses indicates that both species average about 23 kg (51 lb) in weight, but even at mass parity that greater species appears larger and is taller due to its longer legs and neck, whereas the lesser rhea is more compact and more so resembles an outsized, long-necked turkey in build.  Elsewhere, the lesser rhea has been cited with a lower average weight of 16 kg (35 lb). In some areas, male greater rheas weights of up to 35 kg (77 lb) are not uncommon and even females of up to 30 kg (66 lb) have been weighed, both weights higher than the maximum known mass for the lesser rhea. Large males can weigh up to 40 kg (88 lb), stand nearly 1.83 m (6.0 ft) tall and measure over 150 cm (59 in) long, although this is uncommon.
The head and bill are fairly small, the latter measuring 8–10.4 cm (3.1–4.1 in) in length. The legs are long, with the tarsus measuring between 33.5 and 37 cm (13.2 and 14.6 in), and strong and have 22 horizontal plates on the front of the tarsus. They have three toes, and the hind toe is absent. The wings of the American rhea are rather long; the birds use them during running to maintain balance during tight turns, and also during courtship displays.
Greater rheas have a fluffy, tattered-looking plumage, that is gray or brown, with high individual variation, The head, neck, rump, and thighs are feathered. In general, males are darker than females. Even in the wild—particularly in Argentina—leucistic individuals (with white body plumage and blue eyes) as well as albinos occur. Hatchling greater rheas are grey with dark lengthwise stripes.
Greater rhea