The average length of the domestic cat’s tail is 10 inches or 25 centimetres. It is essential to specify the cat species because they vary enormously in length depending on the species. I am assuming that the question relates to domestic cats. I think that you’ll find some variations to the answer on the internet.
Excluding from this discussion the stump-tailed cats – the Manx, Japanese bobtail, American bobtail and Kurilian bobtail – the tails of domestic cats vary slightly in length according to the breed and between individual cats, either purebred or random bred.
Their tails are nearly always more than 8 inches in length (20 centimetres) and less than 12 inches (30 centimetres) with 10 inches (25 centimetres) being the average. There are exceptions, obviously, with some modern, huge Maine Coons having very long plumed tails.
Typically the tail is made up of between 21 and 24 caudal vertebrae. Sometimes, exceptionally there may be as few as 18 or as many as 28 vertebrae. In a normal domestic cat tail the bones reduce in size towards the tip where they are slender rods of bone. The end bone has a conical cap. The tail bones of cats means that they have more bones than humans at 244 (the usual number) compared to our 204.
The original Siamese cats of Siam (Thailand) and even today often had kinked tails. Western breeders did not like them and so they selectively bred the kink out. You can still feel a nobbly bit where the kink should be.
A survey before the mid-1990s found that in Hong Kong about one third (33%) of cats had kinked tail. In Malaysia the percentage was higher at two-thirds (66%) and in Singapore 69 percent of cats had or have kinked tails. I am begin cautious because the status of the kinked tail of the Far Southeast may have changed since Dr Morris mentioned them in his book Cat World.
SOME MORE ON THE CAT’S TAIL: