Instructions
Measure the carapace, or shell, of your red-eared slider. Females tend to be larger than males, and may have a shell length of up to 11 inches. The carapaces of males normally will be no longer than 8 inches.
Observe the length of the turtle's front claws. Males have extremely long front claws, which are noticeably longer than those of females.
Turn the red-eared slider over to observe the plastron (the underside of the shell). If the plastron is slightly concave (curving inward), then the turtle is likely a male. If the plastron is slightly convex (curving outward), then the turtle is likely female. In some cases, the plastron of both males and females will be flat.
Compare the tail sizes of your turtles, if you have more than one. Even though males have a smaller body than females, their tails will be thicker and longer than those of females.
Measure the distance from the cloaca (vent) to the shell. In males, the cloaca tends to be farther from the shell (towards the tip of the tail), while in females the cloaca is closer to the shell.
How to Tell if Your Red-Eared Slider Turtle is Male or Female
It's not easy to distinguish between male and female red-eared sliders. Unlike mammals that have obvious sex differences, turtles' sex organs are completely internal. The most accurate way to sex a red-eared slider is to have a reptile veterinarian insert a probe into the animal's vent. This technique can be dangerous, though, and should only be performed by experienced professionals. Luckily, there are a few ways for pet owners to guess fairly accurately the sex of their red-eared sliders without having to go through this process.