I have an African mud turtle that I keep in a 55. She is about 2 years old and is not really all that big, I would give you an inch comparison but I SUCK at that type of thing My turtle has to go to the vet regularly as she developed a condition with her nose and one of her nostrils is completely stopped up, vet says it is not uncommon in these types of turtles. She does like to stay underwater most of the time hiding in a make-shift bedroom that I made by cutting the end out of a rectangular plastic container.