Cat Brain Size: How Big Is a Cat's Brain, and How Many Neurons?

Cat brain size, in the one cat measured: the brain weighed about 35 g, around 0.8% of its 4.5 kg body. It held 1.2 billion neurons, 250 million of them in the cerebral cortex. By weight that is about half a lime. A dog's brain was 1.7 to 3.3 times heavier, and a human brain holds about 86 billion neurons. All of the cat figures come from a single animal.

Below: how big and heavy a cat's brain is, how many neurons it holds, and how it compares with a dog's and a human's. Then what size cannot tell you about a cat's mind. These figures are about size and cell counts only. No test gives a cat an IQ.

How big and heavy is a cat's brain?

A cat's brain weighed about 35 g in the only cat in the best neuron-counting study we found. Jardim-Messeder and colleagues (Frontiers in Neuroanatomy, 2017) weighed the brain of a captive-bred cat at 34.858 g, with 24.176 g of that in the cerebral cortex. The cat weighed 4.5 kg. By our arithmetic the brain was 0.8% of its body weight, and the cortex was 69% of the brain.

For scale, the study's eight species ran from a 5.4 g ferret brain to a 315.0 g brown bear brain, so the cat sits in the lighter half.

One cat is not a species average. The team analysed one brain hemisphere from a single cat, so treat 35 g as one data point, not a rule for every cat. Many people search what size is a cats brain and expect a range. This study gives one cat, so we cannot give a range.

How does the size of a cat's brain compare with fruit?

By weight, a cat's brain is about half of a lime. People who search for the size of cats brain compared to fruit want a quick picture, and a lime is a fair one. The USDA lists a raw lime two inches across at 67 g, and 34.858 g is 52% of that. This is a weight comparison, not a volume or shape comparison.

For scale at the other end, an adult human brain weighs about 1.3 to 1.5 kg on the two figures our own guides use. That is roughly 38 to 43 times the cat's, by our arithmetic. Our human brain facts guide explains where the human weights come from.

How many neurons does a cat's brain have?

The cat's brain held about 1.2 billion neurons, and 250 million of them were in the cerebral cortex. The cortex is the folded outer layer of the brain. In this cat the cortex held 21% of the neurons, by our arithmetic. Azevedo and colleagues found 19% in the human brain (Journal of Comparative Neurology, 2009).

Most of the rest sat in the cerebellum. The paper gives 3.8 cerebellar neurons for every cortical neuron in the cat, which is about 950 million (our arithmetic). Together with the cortex that comes to the 1.2 billion total.

How does a cat's brain compare with a dog's and a human's?

A cat's brain is lighter than a dog's, holds fewer neurons, and is far smaller than a human's. Here is the cat brain size comparison as the 2017 paper reports it, with the human figures from Azevedo and colleagues.

• Cat (one animal, 4.5 kg): brain 34.9 g; 1.2 billion neurons; cortex 24.2 g with 250 million
• Smaller dog (mixed breed, 7.45 kg): brain 58.4 g; 1.8 billion neurons; cortex 46.2 g with 429 million
• Golden retriever (32 kg): brain 114.5 g; 2.6 billion neurons; cortex 84.8 g with 623 million
• Raccoon (two animals, average): a cat-sized cortex of about 24 g with 438 million neurons
• Brown bear (one animal, 350 kg): cortex 222.0 g with 251 million neurons
• Human (adult male average): about 86 billion neurons, about 16 billion of them (19%) in the cortex

The two dog brains were 1.7 and 3.3 times as heavy as the cat's. They held 1.5 and 2.2 times as many neurons overall, and 1.7 and 2.5 times as many in the cortex. Note that the smaller dog's brain was the same 0.8% of its body weight as the cat's, while the retriever's was 0.4%.

For cat brain vs human brain, the human has about 72 times the cat's neurons overall and about 64 times in the cortex, by our arithmetic. Our guide to human brain vs dog brain gives the full side-by-side, and the koala brain vs human brain page shows how far weight and neurons can drift apart.

Does a cat's brain size track its body size?

Only loosely. Across the eight carnivorans in the study, body mass varied 437.5-fold between the 0.8 kg ferret and the 350 kg brown bear. Brain mass varied only 58.0-fold, and the number of brain neurons only 23.7-fold. Big bodies get bigger brains, but not in proportion, and neuron counts rise more slowly still.

The authors' reading of this is a cost argument. Neurons are expensive to run, and the abstract says large carnivorans appear vulnerable to metabolic limits that impose a trade-off between body size and the number of cortical neurons. That is their interpretation of the pattern. A cat sits in the middle of the range, which is why a cat brain size comparison with a lion or a bear is so lopsided.

Does a bigger brain make a smarter cat?

No study we read shows that it does. The 2017 authors write that any argument about cat and dog cognition is "largely a matter of opinion" until direct comparisons of cognitive ability are made. They found more cortical neurons in dogs, which may fit owners' impressions that dogs are easier to train, and add that cat owners would protest, rightly so.

Size is a poor guide even to neuron counts. The brown bear's cortex, at 222.0 g, held 251 million neurons, the same as the cat's 24.2 g cortex. A raccoon's cat-sized brain held 438 million cortical neurons, almost 1.8 times the cat's. In people, brain volume and IQ correlate at only r = .24 across 88 studies, as our guide to brain size and IQ explains.

So a cat has no IQ score. Our cat IQ guide covers what cat studies do measure, and the guide to the smartest breed of cat shows what a breed ranking can and cannot say. For other animals, see our dog IQ page and the smartest animals research. A human IQ score is compared with a norm group, which our IQ percentile calculator turns into a percentile.

To see how your own reasoning compares with other adults, take the IQ Metrics test.

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