The American toad is among some amphibian species whose outward physical characteristics make it hard to determine males from females. It's easier to distinguish male from female if you have others with which to compare; but you can look for a handful of general telltales nonetheless.
Characteristics for Consideration
Only male American toads (Anaxyrus [Bufo] americanus) call for mates, so if you encounter a frog singing, you know he's a male. Possibly associated with their vocal behavior, male frogs have dark-colored throats while the throats of females are light in color. Female American toads grow much larger than males, and if you find one that exceeds 3 1/2 inches in length, it is most likely female. During the breeding season, male American toads develop enlarged forearms, which help them to clasp females for amplexus. Though all American toads are covered in small bumps, females are often much bumpier than the males are.