Mature male bog turtles have an average length of while the average female length is (straight carapace measurement). The males have a larger average body size than females, likely to facilitate males during male–male interactions during mate selection. The female has a wider and higher shell than the male, but the male's head is squared and larger than a female's of the same age. The plastron of the male looks slightly concave while the female's is flat. The male's tail is longer and thicker than the female's. The cloaca is further towards the end of the tail of the male bog turtle, while the female's cloaca is positioned inside the plastron. Juveniles are very difficult to sex.