The capybara has a heavy, barrel-shaped body and short head, with reddish-brown fur on the upper part of its body that turns yellowish-brown underneath. Its sweat glands can be found in the surface of the hairy portions of its skin, an unusual trait among rodents. The animal lacks down hair, and its guard hair differs little from over hair. Adult capybaras grow to 106 to 134 cm (3.48 to 4.40 ft) in length, stand 50 to 62 cm (20 to 24 in) tall at the withers, and typically weigh 35 to 66 kg (77 to 146 lb), with an average in the Venezuelan llanos of 48.9 kg (108 lb).Females are slightly heavier than males. The top recorded weights are 91 kg (201 lb) for a wild female from Brazil and 73.5 kg (162 lb) for a wild male from Uruguay. Also, an 81 kg individual was reported in São Paulo in 2001 or 2002. The dental formula is 1.0.1.3 1.0.1.3 . Capybaras have slightly webbed feet and vestigial tails. Their hind legs are slightly longer than their forelegs; they have three toes on their rear feet and four toes on their front feet. Their muzzles are blunt, with nostrils, and the eyes and ears are near the top of their heads. Its karyotype has 2n = 66 and FN = 102, meaning it has 66 chromosomes with a total of 102 arms.
Capybaras are herbivores, grazing mainly on grasses and aquatic plants, as well as fruit and tree bark. They are very selective feeders and feed on the leaves of one species and disregard other species surrounding it. They eat a greater variety of plants during the dry season, as fewer plants are available. While they eat grass during the wet season, they have to switch to more abundant reeds during the dry season. Plants that capybaras eat during the summer lose their nutritional value in the winter, so they are not consumed at that time. The capybara's jaw hinge is not perpendicular, so they chew food by grinding back-and-forth rather than side-to-side. Capybaras are autocoprophagous,[28] meaning they eat their own feces as a source of bacterial gut flora, to help digest the cellulose in the grass that forms their normal diet, and to extract the maximum protein and vitamins from their food. They also regurgitate food to masticate again, similar to cud-chewing by cattle. Like other rodents, a capybara's front teeth grow continually to compensate for the constant wear from eating grasses; their cheek teeth also grow continuously.