The emu is the second tallest bird in the world, only being exceeded in height by the ostrich. Individuals can reach up to 59 to 75 inches in height. Measured from the bill to the tail, EMU’s range in length from 55 to 65 inches, with males averaging 58.5 inches and females averaging 61.7 inches. Emus are the fourth or fifth heaviest living bird after the two species of ostrich and two larger species of cassowary, weighing slightly more on average than an emperor penguin. Adult emus weigh between 40 and 132 pounds, with an average of 69 and 82 pounds in males and females, respectively. Females are usually slightly larger than males and are substantially wider across the rump.

Emus have three toes on each foot in a tridactyl arrangement, which is an adaptation for running and is seen in other birds, such as bustards and quails. The ostrich has two toes on each foot.

Although flightless, emus have vestigial wings, the wing chord measuring around 8 inches, and each wing having a small claw at the tip. Emus flap their wings when running, perhaps as a means of stabilizing themselves when moving fast. They have long necks and legs, and can run at speeds of 30 mph due to their highly specialized pelvic limb musculature. Their feet have only three toes and a similarly reduced number of bones and associated foot muscles; emus are unique among birds in that their gastrocnemius muscles in the back of the lower legs have four bellies instead of the usual three. The pelvic limb muscles of emus contribute a similar proportion of the total body mass as do the flight muscles of flying birds. When walking, the emu takes strides of about 3.3 feet, but at full gallop, a stride can be as long as 9 feet. Its legs are devoid of feathers and underneath its feet are thick, cushioned pads.

Emus have good eyesight and hearing, which allows them to detect threats at some distance.

The neck of the emu is pale blue and shows through its sparse feathers. They have grey-brown plumage of shaggy appearance; the shafts and the tips of the feathers are black. Solar radiation is absorbed by the tips, and the inner plumage insulates the skin. This prevents the birds from overheating, allowing them to be active during the heat of the day. A unique feature of the emu feather is the double rachis emerging from a single shaft. Both of the rachis have the same length, and the texture is variable; the area near the skin is rather furry, but the more distant ends resemble grass.[7] The sexes are similar in appearance, although the male's penis can become visible when he urinates and defecates. The plumage varies in color due to environmental factors, giving the bird a natural camouflage. Feathers of emus in more arid areas with red soils have a rufous tint while birds residing in damp conditions are generally darker in hue. The juvenile plumage develops at about three months and is blackish finely barred with brown, with the head and neck being especially dark. The facial feathers gradually thin to expose the bluish skin. The adult plumage has developed by about fifteen months.

The eyes of an emu are protected by nictitating membranes. These are translucent, secondary eyelids that move horizontally from the inside edge of the eye to the outside edge. They function as visors to protect the eyes from the dust that is prevalent in windy arid regions. Emus have a tracheal pouch, which becomes more prominent during the mating season. At more than 12 inches in length, it is quite spacious; it has a thin wall, and an opening 3 inches long.