How to Determine the Sex of a Cat
To determine the sex of a cat, approach the animal carefully and slowly to let it get comfortable with you before you pick it up. Once you have the cat in your arms, hold it with one hand so that its paws are facing the ground, and then gently lift its tail so you can see the genital area. Look at this area to see if the cat has a scrotum, which will look like 2 hairy bumps under the anus. If it does, the cat is male. If the cat doesn't have a scrotum and you can see an anus and a urinary tract opening, the cat is female.
Approach the cat or kitten with care. To ascertain the sex of a cat or kitten, it's necessary to pick the cat up. Some cats don't like to be handled, so take a little time to let him or her get comfortable around you. Stand or crouch near the cat and let him or her approach you. When the cat comes close, let him or her sniff your hand. If the cat seems nervous, you may have to come back later or have a partner help you with the next step. Lift the cat's tail. Gently pick up the cat and cradle him or her in one arm. Use your free hand to lift the tail so you can examine the genital area. If the cat doesn't mind being handled, this may be easiest to perform while sitting on a chair or the couch, so you don't have to worry about dropping the cat. If you're working with a partner, have the partner hold the cat securely in both arms while you lift the tail. If the cat avoids having his or her tail lifted, try scratching him or her in the area where the tail meets the back. Cats usually lift their tails when they are touched in this spot. Look for genitalia characteristic of a male cat. The surest way to tell the difference between a male and female cat is by examining the cat's physical features below its tail. Begin by looking for male genital features, which can be somewhat easier to spot. A male cat will have an anus, scrotum, and penis, while a female cat will have only an anus and urinary tract opening. In an entire (or tom) cat, the scrotum is covered with fur and contains two testicles, each typically ranging in size from the size of cherry pits to actual cherries. The scrotum sticks out from the male cat's rear as a fairly obvious pair of bumps. If the cat has long fur, this can make the scrotum more difficult to see, in which case try dampening the fur with water to flatten it down and make the scrotum more obvious. A neutered male cat will still have a scrotum, though it will typically be smaller. The penis is sited below the scrotum, beneath the skin, and exits at a small furry mound between the cat's thighs. You might imagine a male cat's genitalia resembling a colon (:). A male cat's anus and urinary tract opening are at least 1 inch (2.5 cm) apart, or ⁄ 2 inch (1.3 cm) for kittens. Look for genitalia characteristic of a female cat. If the cat's genitalia doesn't appear to match that of a male cat, begin looking for female traits. A female cat will have an anus and a urinary tract opening/vulva, with the vulva in the shape of a vertical slit. You can imagine a female cat's genitalia as resembling a semi-colon (;). A female cat will have a shorter distance between anus and vulva, typically about ⁄ 2 inch (1.3 cm) apart. Check the color. If you have a litter of kittens, look at the color of the cats; some cat colorations are sex-specific and can help you determine the sex of the cat. Cats that are calico or tortoiseshell colored are typically female. More orange or ginger colored cats are male than female, but this is not an accurate way to determine a cat's sex. Watch for sex-specific behaviors among intact (not neutered or spayed) cats. It's easier to tell the sex of intact cats, since they naturally display the habits and characteristics of their sex. Male cats that have not been neutered tend to be more aggressive than females and to have larger heads and thick skin. They like to roam, sometimes leaving for a few days at a time. They mark their territory by spraying it with strong-smelling urine. Female cats are less likely to spray their surroundings. Watch for signs that the cat is in heat or is or has been pregnant. Female cats that have not been spayed will go into heat, a state of fertility that enables them to become pregnant, every 3-5 weeks during warm weather (or in a house that's climate controlled). Cats in heat display recognizable behaviors: Making vocal sounds to attract males. The cat may sound like it is in pain or whining. Moving the tail to the side to show genitalia or crouching into a receptive posture. The vulva may be secreting a clear discharge. Rubbing up against inanimate objects, owners, or other animals more than usual. Pregnant female cats have low-hanging, distended bellies. Female cats that have given birth may have nipples that protrude from their bellies. Be careful when using nipples to determine sex, since both male and female cats have nipples. 
Approach the cat or kitten with care. Lift the cat's tail. Look for genitalia characteristic of a male cat. Look for genitalia characteristic of a female cat. Check the color. Watch for sex-specific behaviors among intact (not neutered or spayed) cats. Watch for signs that the cat is in heat or is or has been pregnant. 