How Big and Fast Was T. rex? Size, Bite Force and Top Speed

It is the most famous dinosaur of all: the “tyrant lizard king”, star of museums and films. But how much of its popular image is true? Scientists have studied T. rex bones, footprints and computer models to work out how big it really was, how hard it bit and how fast it could move.

The fact file

Tyrannosaurus rex lived in what is now western North America, about 68 to 66 million years ago. It was one of the last non-bird dinosaurs, alive right up to the asteroid impact. That means T. rex lived closer in time to us than to Stegosaurus, which died out around 80 million years before it appeared.

Large adults were about 12 metres long from snout to tail and about 4 metres tall at the hips. Estimates of their weight vary, but most fall at 8 tonnes or more, heavier than an African elephant. The skull alone was about 1.5 metres long.

The strongest bite on land

T. rex had about 60 thick, banana-sized teeth, serrated like steak knives. In 2012 Karl Bates and Peter Falkingham built a computer model of its skull and jaw muscles. They estimated its bite force at 35,000 to 57,000 newtons at the back teeth, the strongest of any known land animal, living or extinct. For comparison, an adult human bite is around 1,000 newtons.

Fossil evidence agrees. Bones of other dinosaurs show deep T. rex tooth punctures, and fossil dung contains crushed bone fragments. T. rex did not just tear flesh; it crunched bone.

Could it outrun a car?

In the original Jurassic Park film, a T. rex chases a jeep at high speed. The science says otherwise.

In 2017, a team led by William Sellers built a detailed computer model of T. rex’s skeleton and muscles and checked how much stress its bones could take. At higher speeds, the forces on the leg bones became too great: the bones would have broken. The model suggested a top speed of around 20 kilometres per hour, more like a brisk jog than a sprint, and that T. rex could not truly run, with both feet off the ground at once.

In 2021, a study led by Pasha van Bijlert estimated its comfortable walking speed by looking at how its heavy tail would have swung with each step. The answer: about 4.6 kilometres per hour, roughly the walking speed of a person. Other estimates vary, but a car on a road would leave T. rex far behind.

Arms, eyes and noses

T. rex’s arms were only about 1 metre long, tiny compared with its body, yet muscular and with two clawed fingers. What they were used for is still debated. Its eyes faced forward enough to give good depth perception, and its brain had large areas for smell. Its skin, from fossil impressions, was covered in small scales.

How long did it live?

Bones, like trees, can have growth rings. By counting them, scientists found that T. rex grew extremely fast as a teenager, gaining more than a tonne a year at its peak. Few individuals lived beyond about 30 years. The famous skeleton Sue, in Chicago’s Field Museum, died at around 30.

In short

• T. rex lived in North America about 68–66 million years ago.
• Adults were about 12 metres long and probably weighed 8 tonnes or more.
• Its bite force was about 35,000–57,000 newtons, the strongest of any land animal.
• Models suggest a top speed of only about 20 km/h and a walking speed of about 4.6 km/h.
• Its tiny arms were muscular, but their purpose is still debated.
• T. rex grew very fast and rarely lived beyond about 30 years.