Capybaras have heavy, barrel-shaped bodies and short heads with reddish-brown fur on the upper part of their body that turns yellowish-brown underneath. Adult capybaras may grow to 130 centimeters (4.3 ft) and 50 centimeters (1.6 ft) tall, weighing up to 65 kg (140 lbs). Capybaras have slightly webbed feet and no tail; their back legs are slightly longer than their front legs and their muzzles are blunt with eyes, nostrils, and ears on top of their head. Capybaras have 20 teeth. Females are slightly heavier than males.

Though now extinct, there once existed larger capybaras that were eight times the size of modern capybaras (these rodents would have been larger than a grizzly bear).

Capybara are semi-aquatic mammals found wild in much of South America (including Panama, Colombia, Venezuela, Brazil, Argentina, French Guyana, Uruguay, Peru, and Paraguay) in densely forested areas near bodies of water, such as lakes, rivers, swamps, ponds and marshes, such as flooded savanna and along rivers in tropical forest. They roam in home ranges of 25–50 acres (10–20 ha).