Capybaras are the world's largest rodents. They resemble guinea pigs but are much larger. They have large, broad heads with short, rounded ears and eyes placed far back on the head. Their snout is heavy and blunt with a large upper lip and big nostrils. Their neck and legs are short. Adults weigh between 110 and 173.8 pounds (50 to 79 kilograms) and have a head and body length of 39.4 to 51.2 inches (100 to 130 centimeters).
Capybaras have four toes on their front legs and three on their back legs, all with short and strong claws. Their feet are partially webbed, making them good swimmers. Their front legs are shorter than the hind legs.
Their bodies are covered with short, coarse fur ranging in color from reddish brown to grey on the upper body and light yellow to brown on the lower body. Adult males have a bare, raised area at the top of their snouts that contains a scent gland that is used to mark their territories. The tail is short and not functional. Female capybaras are usually larger than males.