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There are 2 species - the Western and Eastern gorillas, and both species have silverback males. The larger of the two is the Eastern Gorilla. The maximum size of a male gorilla can be over 225 kg (500 lb) and 1.83 m (6 ft) in the wild, with much heavier weights recorded in captivity. (Although I can't find a decent reference to the recorded sizes either.)
1 As compared to the adult male gorillas, the females have shorter arm spans.  The silverback gorillas weigh around 230 kg (510 lb), with the length of 1.8 meters (5 ft 11 inches). The heavy gorillas can be as much as 270 kg (600 lb).