Side view of mature adult showing characteristic "S" neck Black Swans are primarily black-feathered birds, with white flight feathers. The bill is bright red, with a pale bar and tip; and legs and feet are greyish-black. Cobs (males) are slightly larger than pens (females), with a longer and straighter bill. Cygnets (immature birds) are a greyish-brown with pale-edged feathers.
A mature Black Swan measures between 110 and 142 centimetres (43 and 56 in) in length and weighs 3.7–9 kilograms (8.2–20 lb). Its wing span is between 1.6 and 2 metres (5.2 and 6.6 ft). The neck is long (relatively the longest neck among the swans) and curved in an "S"-shape.