In the finale of Game of Thrones’ last season, Daenerys Targaryen is appalled at the presentation of a young girl’s charred bones, ostensibly the work of her largest dragon, Drogon. It’s the final atrocity she will permit her ravenous pets. She chains up the other two, but Drogon evades her. Dany then vows that no more bones will be laid at her feet. But dragons have to eat – at least three people a day.

How do you find the dietary requirements of a dragon? Use a suitable comparison. For that, we need Drogon’s size. According to Game of Thrones’ visual effects supervisor Joe Bauer, “[Drogon] is about 40 feet long and 20 percent bigger than the other two dragons” in season five.

Metabolism is important too. If Drogon had the feeding habits of a hummingbird, it would wipe out Westeros. If it had a crocodile’s energy requirements, it could eat a person or two a month and be fine. Maybe Drogon is something in between. A Tyrannosaurus rex – an ancient, reptilian predator that was “warm-blooded” (more metabolically active than a snake, for example) – isn’t the least plausible dragon analog. Even the sizes match up, as T. rex may have gotten as large as 40-feet long from steak knife teeth to tail.

A human body isn’t exactly a Big Mac, but it does contain a ton of calories. Randall Munroe of the brilliant xkcd estimates that eating an average human would be equivalent to eating 80 burgers, or 110,000 calories of energy. Munroe, collecting data from various sources, also figures that if T. rex needed maybe 40,000 calories a day to live, then a tyrant lizard could get by on one person every two to three days.

How does Drogon stack up against other fantasy dragons? (Image: The Daily Dot)

We could stop there and say that because a similarly sized reptilian predator could live on this diet, so could Drogon. However, Drogon doesn’t move like a Tyrannosaurus. In fact, you hardly see Drogon do anything but fly around in Game of Thrones. Flying is energy-intensive, and that would require more tasty sheep/fish/people.

There’s a reason why birds don’t get very big – more weight requires more lift, and more lift means bigger wings, which means more weight, and so on. A 40-foot long dragon would require enormous wings (and the bones/muscles/connective tissues to stand up to the forces involved). Think of it this way: the Andean condor, one of the largest birds on the planet, weighs less than a few bags of groceries and still needs a 10-foot wingspan.

But if we go ahead and assume Drogon’s football field-sized wingspan is physically possible, we also have to guess that it requires much more daily energy than T. rex would. One nerdy analysis of dragon flight calculates that a dragon, one much smaller than Drogon, might need 250,000 calories a day just to power all the muscle required to fly.

Adding everything together – the energy-hungry flight muscles, the appetite of T. rex, and some additional caloric requirements just to be safe – Drogon would need perhaps 400,000+ calories per day to terrorize Westeros, or at least three well-fed humans.

Unfortunately for Daenerys, roughly scaling down the caloric content of an adult, Drogon would need to eat nine to ten children per day to sustain it. We’d all hope that sheep or fish are what’s on the menu as Drogon roams free, but we know better. This is Game of Thrones, and valar morghulis.

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Kyle Hill is the Science Editor at Nerdist Industries. Follow on Twitter @Sci_Phile.