How heavy is a silverback gorilla?

Figures vary from source to source, but they cluster around 140 to 170 kg (310 to 375 lb) for a wild adult male. San Diego Zoo Wildlife Alliance gives males 136 to 181 kg (300 to 400 lb), and the Smithsonian’s National Zoo says western lowland males average about 136 kg (300 lb) and can reach 227 kg (500 lb). Studies that actually weighed wild males also disagree: Colin Groves (1970) averaged 144 kg across 42 males, while Smith and Jungers (1997) got 169 kg from 19. A silverback of 160 kg sits right in the middle.

Females are much smaller, usually around 70 to 98 kg (155 to 215 lb), so a big male weighs about twice as much as the females in his group. Males only become silverbacks once they are fully grown, at about 12 or 13 years old, when the hair on their back turns grey.

There are two species, eastern and western gorillas, each with two subspecies. Guinness World Records names the eastern lowland (Grauer’s) gorilla of the Democratic Republic of the Congo as the largest living primate, with males standing about 1.75 m (5 ft 9 in) tall and weighing up to 210 kg (463 lb).

Its close relative, the mountain gorilla, is a little smaller: males average about 155 kg, and the African Wildlife Foundation gives the subspecies a range of 135 to 220 kg (300 to 485 lb). Western lowland gorillas, the ones you see in almost every zoo, are usually described as the smallest. In practice the subspecies overlap a lot, and some averages rest on only a handful of weighed animals.

Zoo food has traditionally been richer than the leaves, stems and fruit wild gorillas eat, and zoo gorillas spend less time foraging. A 2023 study by Herman Pontzer found that female western lowland gorillas in captivity average about 94 kg, around 31% more than wild females. Males, at about 171 kg, came out roughly the same as wild ones on average, but a few individuals have grown very heavy.

Diet makes a real difference. When Cleveland Metroparks Zoo moved its males onto a diet of lettuce, leafy greens, hay and branches, they lost nearly 65 lb (29 kg) each in a year while eating twice as many calories. Heart disease is the leading killer of male western lowland gorillas in North American zoos, which is one reason zoos now watch their weight closely.

The heaviest wild gorilla on record was a 1.83 m (6 ft) silverback shot in Ambam, Cameroon, which weighed 267 kg (589 lb). The tallest, shot in the Kivu region of the eastern Congo in May 1938, stood 1.95 m (6 ft 5 in) and weighed 219 kg (483 lb).

In zoos, Samson of the Milwaukee County Zoo was recognized in 1971 as the heaviest living gorilla in captivity at 652 lb (296 kg). He had arrived in Milwaukee in 1950 as a baby of nearly 13 lb, and his keeper later cut his daily loaf of bread in half. He died of a heart attack in 1981. An older Guinness animal record book mentions captive males of up to 310 kg (683 lb).