With a little help from the “Jurassic Park” franchise, the Tyrannosaurus rex has become perhaps the most well-known dinosaur on Earth. But until only recently, paleontologists had no solid estimations regarding the number of T. rex that existed during their earthly reign some 68 million years ago.

Through a series of calculations based on the dinosaur’s body size, energy needs and sexual maturity, a research team at the University of California, Berkeley estimated how many T. rex lived on the Earth and published their findings in the journal Science, HuffPost reports.

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The researchers also adhered to a doctrine known as Damuth’s law while estimating the size of T. rex populations, Reuters adds. According to Damuth’s law, there’s a correlation between animal size and population size — the bigger an animal is, the fewer individuals of that species tend to exist at a given time.

Reuters reports that the analysis determined about 2.5 billion T. rex lived on Earth across 127,000 generations (2.4 million years), which means approximately 20,000 fully grown T. rex inhabited the planet together at once. Though, The Associated Press playfully pointed out that the estimations feature a margin of error that’s the size of a T. rex.

“That’s a lot of jaws. ... That’s a lot of teeth. That’s a lot of claws.” said Charles Marshall, the study’s lead author and the director of the University of California Museum of Paleontology (via HuffPost).

Kristi Curry Rogers, a paleobiologist at Macalester College, added, “Probably like a lot of people, I literally did a double-take to make sure that my eyes hadn’t deceived me when I first read that 2.5 billion T. rexes have ever lived” (via HuffPost).

SciTechDaily.com reports that the results suggest only 1 in about 80 million T. rex have survived the eons to become fossilized remains.