The best way to determine the sex of male and female kittens is to rest the kittens on their bellies on a warm (not hot) towel, gently lift their tails and examine their genitals. Several differences exist between male and female kittens, even newborn kittens, which you can look out for when sexing kittens.
1. Examine the distance between the kitten's anus and genitals (vulva in females and penis in males).
Look at the pictures below. These are close-up photographs of the anuses and genitalia of two individual 3-week-old kittens. The first kitten (kitten on the left) is a young male and the kitten beside it (on the right) is a young female.
What you will notice from these two images is that the distance between the anus and the penis of the young male kitten (image 1) is significantly greater than the distance between the anus and vulva of the young female kitten (image 2). I have labeled the images below (the same images as those above) to more clearly illustrate these differences for you.
2. Examine the shape of the kitten's genital opening (vulva or penis).
Look at the pictures below. These are close-up photos of the genitalia of two individual 3-week-old kittens. The first kitten is a young male and the kitten beside it is a young female.
What you will notice from these two images is that the genital opening (penis or penis-sheath opening)of the young male kitten (image 1) is shaped like a small circular dot, whereas the genital opening (vulva) of the young female kitten (image 2) is shaped like a vertical slit. I have labeled the images below (the same images as those above) to more clearly illustrate these differences for you.
3. A bulging scrotal sac should start to become visible in male cats from about 10-12 weeks of age.
The scrotal sac or scrotum is a bulging out-pouching of skin that contains the testicles of male cats. It is located between the anus and penis of male kittens and cats. In a newborn male kitten, the testicles are tiny and the scrotal sac barely recognizable (e.g. you can not see the scrotal sac in the pictures of the 3-week-old male kittens above), however, as the kitten gets older (10 weeks +) and its testicles start to enlarge, the scrotal sac starts to protrude outwards and become very obvious. If you can see a clearly defined scrotal sac, the kitten or cat is a male.
Image: The scrotal sac is not clearly visible in this 3-week-old male kitten because its testicles are very small and its scrotum not yet fully developed.
Image: This is an image of a 12-week-old kitten who is currently anesthetized before being neutered. To orientate you - the kitten is lying on its back. You can already see a small, but obvious, bulge between this kitten's anus and penis. This is the scrotum with testicles inside. This kitten is therefore a male.
Image: This is a picture of an 8-month-old male cat who is currently anesthetized before being neutered. To orientate you - the tomcat is lying on its back. The scrotum (the bit resting upon the pink surgical swabs)is well-developed and very obvious with two side-by-side, individual bumps inside it: the two testicles. The penis too is well-developed and somewhat pendulous. If you see a cat with these genital features, it is definitely a boy.
Author's note: Kittens or cats with retained or undescended testicles (cryptorchid cats)will not develop an obviously enlarged or pendulous scrotum.
4. Testicles should be palpable in the male scrotum from the time of birth
The testicles of male kittens descend into the scrotal sac just before the kitten being born. It is therefore possible for testicles to be palpated in the scrotal sac regions of very young male kittens, even if the scrotum sac itself has not yet obviously enlarged. For example, testes were clearly palpate in the scrotal region of the three-week-old male kitten pictured above, even though no scrotum could be seen.
To feel for testicles: gently but firmly place your fore-finger and thumb on either side of the kitten’s scrotum (or, in a very young kitten, where the scrotum should be) and slowly and gently bring your fingers together in a pincer-action, sliding your finger-tips firmly along the skin of the kitten's scrotum. If the kitten is a male, what you should feel between your fingers are two smooth, ovoid, small (approx 3-5mm diameter in a 3-week old kitten)objects located side-by-side underneath the skin of the scrotal sac region. These are the testicles. Often you'll only feel these testicles one at a time (it is hard to grab both at once in a small male kitten) and often these testes will deftly slide away from your finger-tips when pressed (they are tricky to grasp hold of and feel like small peas rolling away under your fingers).
Image: This pic shows where to palpate for testicles in a male kitten or cat.
Author's note: You may not be able to feel the testicles of kittens or cats with retained or undescended testicles (cryptorchid cats) because their testicles will be located ahead of the scrotum, perhaps even within the cat's abdomen.
5. Color can be your guide.
Occasionally, the fur color of your cat or kitten can give you some indication as to the sex of the kitten.
Tortoiseshell cats (cats with three colors - white, black, and orange) are almost always female.
Ginger cats are predominantly male, but can sometimes be female. Ginger is a less reliable color indicator of feline sex.