Hypothetically, how much do you think a (fictional) dragon eats?

[Coluber42]

I don't watch or read Game of Thrones, so here are my thoughts about generic dragons in general:

1. If they breath fire, they must have an extremely high internal body temperature, which presumably has high metabolic demands to maintain, even assuming that their skin has exceptional insulating properties.

2. However, many dragons do appear to have extended brumation periods on top of their piles of gold. Their metabolic requirements are presumably much lower during these times, and they seem to thrive and even grow on just the occasional knight or hero.

3. I also have to assume that a dragon requires much more iron and other metals in its diet than most animals, due to its high internal temperature and probably also to reinforce its bones and muscles in order for such a large animal to be able to fly. That's why they need a pile of gold in order to attract knights: they need the nutritional content of the plate armor, chain mail, etc. Princesses appear to fill the same function.

4. Speaking of flight, for a large animal to get off the ground requires a LOT of energy. I think Smaug in Lord of the Rings is roughly in the same ballpark, size-wise, as a 747. But he appears to be about the upper limit, size-wise, for fictional dragons that fly. Wagner's Fafner is said to be giant (and was a giant before he was a dragon...) but he's still small enough for Siegfried to slay with a sword. So dragons do seem to reach an adult size somewhere between the size of a horse and the size of a 747.
A 747 uses something like 1500 gallons of fuel during takeoff alone, or about 50 trillion calories, or about 8500 elephants (apparently jet fuel is more energy dense than elephants). Dragons don't go anywhere near as fast or as high, and for the sake of argument we'll say they're also much lighter than a similarly sized aircraft. So if they're a hundred times as efficient as a 747, Smaug would still burn 85 elephants' worth of calories just to get airborn. All that swooping around presumably burns a good bit too. My guess is that a dragon of Smaug's size would pretty much have to be able to slow down its metabolism and use the hoard as bait for knights and heroes, because going on a rampage in order to catch large game would have such high caloric costs that the dragon like Smaug would have to eat like an entire herd of wildebeest in order to come out ahead by the time it got home.

But dragons more the size of horses or elephants or small whales would have much more manageable caloric requirements, although flight would still be pretty demanding.

So in conclusion, a dragon that is very active, able to breathe fire, able to take off from the ground and perform complex aerial maneuvers, etc, probably has very high caloric requirements on the order of consuming its own weight in energy-dense food (e.g, not salad) somewhere between every 12 hours and every week. If it isn't able to brumate "on demand" when its energy stores run low, it probably dies of starvation extremely quickly, like a hummingbird.

However, a dragon that mostly sleeps on top of a hoard of treasure until a meal happens by has much lower requirements and can survive on the occasional knight or hero. Sort of like a ball python with its nose poking out of its hide, waiting for Furry Sir Gallahad the Squeaker to happen by.

Edit: Wow, I am really overthinking this......