It's very difficult to find out the sex of your frog by looking at them.

A good rule of thumb is that if your frog croaks, it is male. And if it doesn't, it is female. Females will only usually croak if they are distressed, and this is more of a 'squawk' than a croak. When males croak, it lasts more than a few seconds and sounds like "WOK WOK WOK WOK WOK WOK".

During the mating season, male frogs do have 'nuptual pads', these are usually small dark brown pads starting at the middle of the inside of the thumb and extending onto part of the inside of the forefinger. The skin on their throats will then loosen and start to develop a shady pigment, usually a purplish brown. Females will get fatter. It's a general observation that females are larger than males but this is not usually a good indicator of sex.