Generally, male and female are judged based on the distance between the cat's anus and urethral opening. The distance between the anus and urethral opening of a female cat is relatively close, while that between the male cat's anus and urethral opening is relatively far. The testicles of male cats are particularly obvious, located directly above the anus, below the urethra, one on both sides, which is the part that produces sperm and secretes and androgens. This method is the easiest to distinguish when a cat becomes an adult. Kittens are not easy to observe because their organs are not fully developed.
If you want to judge a cat's male and female, you can lift the cat's tail and look at the two holes in its butt, the anus on it and the genitals below. The distance between the two holes of the female cat is 1 cm, and the hole below is like a colon; the distance between the male cat is 2 cm, and the hole below is an exclamation mark.
Generally, male cats are larger than female cats, but the difference is not particularly obvious at 2-3 months, so body shape comparisons can only be used as a reference.