How Big Was a T-Rex Brain?

Many of us have heard it said that dinosaurs, despite their often impressive size, were not overly well furnished in the brains department. The phrases such as “a brain the size of a walnut” are often thrown around with dinosaurs, especially the larger species, no doubt in an attempt to create a reaction of shock and surprise in the listener or reader.

An Average T Rex brain was weighed about 1 kg, or 2.2 lbs, about half the size of an average human brain. Although not as intelligent as most modern birds, or animals. it was more intelligent, or at least had a larger brain, than its similar sized contemporary dinosaurs like stegosaurus with a brain 10 times as large.

But how accurate are these claims for possibly the most well-known dinosaur breed, Tyrannosaurus rex? Was this apex predator really just a simpleton with exceptionally sharp teeth and claws but a brain the size of a table tennis ball? We will try to find out more in this article.

Tyrannosaurus T-rex largest meat eating dinosaur
How Big Was a T-Rex Brain

Did T-Rex Have a Big Brain?

Tyrannosaurus rex was a large theropod dinosaur that typically measured up to 40 feet in length and up to 12 feet in height, and typically weighed anywhere from 11,000 to 15,500 pounds. You can read more about how tall and how big a T Rex was here. It may feel intuitive to assume, therefore, that its brain was fairly sizable, but alas that’s not generally how nature works.

A T-rex brain was about 1 kilogram, or 2.2 pounds in weight, about half that of an adult human’s brain. However, we should not take this to mean that the beast was only half as smart as we are. In fact, it has been well documented by paleontologists and others making detailed studies of different dinosaur species over the years that predators such as the T-rex were invariably endowed with larger brains than their herbivore counterparts.

In terms of shape, the T-rex had a fairly large, elongated brain case, which is clear from discovered fossilized remains.

However, the cerebrum was very small, which is why despite its relative size, the brain was not weighty or particularly powerful or complex like the human brain is. This kind of brain setup — large case, small cerebrum — is a fairly common feature of many animal species, past and present.

The brain is a very energy-intensive organ, after all. In the human body, about 25 percent of all our calorie intake goes to supporting the brain, even when the brain itself only represents a tiny fraction of our overall mass. In animals, the smaller brains means more energy where it’s needed elsewhere in the body, and the same was true for the dinosaurs.

T-rex’s brain is believed to be the largest of any other dinosaur of its size and scale. It was larger than the Hadrosaur brain, and bigger than that of an adult Triceratops. The Stegosaurus had a brain weighing just 8 percent that of the T-rex, despite its imposing 5-ton frame, which we also take a look at. here.

T Rex Facts infographic

Brain Aside, Was T-Rex an Intelligent Dinosaur?

So we now know that T-rex did not have a big brain generally speaking and certainly not when compared to its size and mass, but that its brain was actually fairly sizable relatively speaking. Its brain power was certainly enviable in the dinosaur world, assisted by strong binocular vision, likely even vision in color.

When these elements were put together, T-rex was not just fast and powerful, but a smart and capable predator, despite what Hollywood movies may have told us in the past about their physical and cerebral limitations.

While we can speculate on the possible intelligence of T-rex, it’s impossible to say for sure how smart it really was without observing its behavior in real-life conditions. The main evidence for its highly capable nature compared to other dinosaurs comes from evidence of anatomical features, including the brain, but also the apparent binocular vision and enhanced sense of smell.

There are some, for instance, who always theorized that T-rex was more of a scavenger than a true hunter, merely using its sense of smell to detect carrion and move in to scare off other would-be diners in order to enjoy more of the food for itself.

While it’s perfectly possible that a T-rex would never turn down a free meal, more modern discoveries point to the T-rex being a more than capable predator in its own right. Being a predator requires more thought than just scavanging and T Rex had a brain that was certainly capable of that.

For example, closer examination of T-rex nasal structure clearly shows that this beast had a far more advanced sense of smell than previously thought. When one then combines it with the much stronger vision that it possessed compared to older notions, the T-rex becomes a formidable enemy in almost any environment.

As we have mentioned before in another T-rex article, too, the T-rex was also able to swim fairly effectively, therefore being able to chase live prey into water to get the kill when hungry, although not too far as although it could swim, it wouldn’t have been able to hunt effectively in water, no matter how clever it was or wasn’t.

how big was a t Rex Brain

What Was the Most Intelligent Dinosaur?

Although T Rex may have been relatively smart for a dinosaur of its time with a 1 kg (2.2 lb) brain it wasn’t thought to be the smartest dinosaur. As dinosaur size grew, brain size in relation to its body often got smaller.

So there were plenty of smaller dinosaurs, with more need for a more active brain to hunt and evade, alive. the smartest of which is commonly considered the troodon family of dinosaurs. We go into much more detail in our What was the smartest dinosaur article linked below.

The troodon was a theropod that lived during the late cretaceous. it is thought the most intelligent of all dinosaurs due to its brain size being considerably large compared to its size. It had excellent eyesight, smell and hearing and likely lived in packs all of which require a high level of intelligence.

MArc Ford

We have a couple more articles, and more to come, on the intelligence of dinosaurs overall, and of some specific ones, You can jump to these below if you need.

It’s Not the Size, It’s How You Use It

In the end, the size and weight of a T-rex brain was apparently less relevant than its relative power. T-rex did have a relatively large and capable brain compared to many dinosaurs that came before and after it.

The general picture of brain evolution in larger dinosaur species was that the larger the beasts became, the smaller their brains, with large long-necked species like the Brachiosaurus only having a brain about the size of a tennis ball and a body the size of a tennis court!

T-rex, on the other hand, seemed to buck that overall trend, having a relatively large, heavy and capable brain, even with its limited cerebrum. After all, T-rex was still a wild animal, and didn’t require a large cerebrum to achieve its main survival goals.

It was a fearsome, fast, and deadly predator, and the abilities afforded to it by its brain, eyesight, sense of smell and physical build were all part of its reputation as ‘king of the reptiles.’

We have a huge selection or articles to answer the common and some less common questions about the Tyrannosaurus Rex here on the site and to make it easier to access we have them in the table below.

How heavy was T-RexDid T-Rex Ever Eat PlantsT-Rex Vs. MammothDid T-Rex have Bad Eyesight
Did T-Rex RoarHow Tall was T-rexDifferences between T-Rex and VelociraptorDid T-Rex Hunt in packs
T-Rex Vs SpinosaurusHow big was a T-Rex BrainCould T-Rex Swim?Did T-Rex have Wings
Did T-Rex Lay EggsClosest living relative to T-RexTriceratops Vs. T RexHow fast could T-Rex run
How big was a T-RexT Rex Facts


So a T Rex Brain was about 1.1 pounds or 2 kilos in weight, and fair elongated. Although half the size of an average human brain, and much less powerful, for a dinosaur it was no slouch. it is thought that among dinosaurs of its size the Tyrannosaurus Rex was classed as intelligent.

the rule of thumb being the larger the animal the less important a large brain was, no need to hide, move quickly see that well etc. However T Rex cognitive abilities if still less than modern birds was more than enough to spot, ambush and pursue its prey of that time.


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