How long is a tuatara? Adult S. punctatus males measure 61 cm (24 in) in length and females 45 cm (18 in). The San Diego Zoo even cites a length of up to 80 cm (31 in). Males weigh up to 1 kg (2.2 lb), and females up to 0.5 kg (1.1 lb). Brother's Island tuatara are slightly smaller, weighing up to 660 g (1.3 lb).aa