"Pterygotus" was among the largest eurypterids. Isolated fossil remains of a large chelicera (frontal appendage) suggests that the largest known species, "P. grandidentatus", reached a body length of . Several other species, notably "P. impacatus" at and "P. anglicus" at were similarly gigantic. "Pterygotus" was surpassed in size by other giant eurypterids. "Acutiramus" was able to surpass 2 metres (6.6 ft), and "Jaekelopterus" could reach 2.6 metres (8.5 ft). Many species were considerably smaller than the largest species, such as "P. kopaninensis" at .