how can i know whether my turtle is female or male?

chenpan, Greetings! I had two (2) Malayan Box Turtle in the past. The male has a concave plasteron ( The underside portion of the shell) and the female has a slightly convex plasteron. The male is smaller than the female. It took more than 3 years before these signs were obvious to us. I also have five (5) red eared slider turtles but I think they are no longer pure breed because their strip in their head are no longer red in color but somewhat in the shade of orange. Well for the RES, the male grew long nails, thick tails. The plasteron does not have concavity like that of the malayan box turtle for male turtles. The female turtle on the other hand does not show convexity but are larger than the male. It also took almost 3 years to notice the difference. The male when young grows faster than the female and then stop growing when their carapace (the top shell) is almost 4 inches. The female when young grows slowly but when they reach 4 inches then they grow rapidly. Currently the male RES is only 4 inches while the female is 9 inches in length. Determining the sexes of the turtles are different for each type of turtle breed. Ferritic

According to one article on wikipedia, the way to tell is turn the over so the turtle's belly can be seen. If the belly is rounded, you have a female. If the belly is indented (meaning goes in a bit) you have a male. Hope that helps. Another place said that males have a bigger tail than a female; males have a vent about 2/3 away from the shell towards the tip of the tail and the females have it closer to the shell. Male sliders grow long claws on their front legs. These things may take a couple of years to develop so don't expect to tell in a baby turtle... Good luck.