based on some reasearch and other peoples experience the avrage male dovii gets 16-20 inches, avrage 18 inches... I know some get like 8 inches bigger but i am talking about the avrage joe dovii... I don't have experience with a large dovii but i have done lots of reasearch and some people that have raised them many times said this is an AVRAGE... the Huge ones do need tanks way bigger than avrage doviis...