Oh my god finally maths that I'm interested in
Okay, so for the sake of having SOMETHING to work with, lets assume that a fantasy dragon has a similar metabolism to a Komodo dragon.
Komodo dragons are able to eat 80% of their body weight in one sitting, and because of this they are able to survive on just one meal a month.
So, for the sake of the argument I'm going to assume that for a dragon to survive for a month, they'd need to consume about 80% of their body weight in food.
When dragons are first hatched, they're about the size of a cat. The average weight of a housecat (and therefore baby dragon) is about 10lbs/4.5kg, give or take a few pounds.
80% of that is about 8lbs/3.5kg. Lets assume that baby dragons in the wild would hunt down like, mice or rats or birds or whatever. Like, probably their parents would feed them, but we're gonna assume that our baby dragon is an orphan and it needs to get shit done on its own.
The average weight of a house mouse is 18g. 3500g divided by 18g = 194.
So if baby cat-sized dragon wanted to survive on rodents, it would need to eat 194 mice per month.
Sooo... seeing as thats unrealistic as hecc, I'm gonna assume that baby dragons rely heavily on their parents to bring them, like, a hunk of sheep or whatever for them to survive. So orphan baby dragons need to be hardcore as fuck, or they dead.
Also, in case you're curious: average weight of a sheep is 75.5kg. 3.5kg divided by 75.5kg = 0.046. So if Mama Dragon wants to feed baby dragon, all she needs to give it is like 0.46% of a sheep per month. Which is a lot better than 194 mice.
Anyway, baby dragon is older now - a teenager or 'adolescent', or whatevs, and I'm gonna assume that adolescent dragons weigh about the same as an elephant?
The average weight of an African Bush elephant (and therefore adolescent dragon) is bout 6000kg. 80% of that is about 4800kg
4800kg divided by average sheep weight (75.5kg) = 63.5 (we'll round that up to 64)
For an adolescent dragon to survive, he'd need to chow down on about 64 sheep per month.
And then, for a grown up dragon - dragons never stop growing. Ever. So trying to calculate how much an 'average' adult would weigh, or eat, or whatever is like- impossible. Un-doable. I would go crazy trying.
But, for the sake of dragon science, I will use the loosest, most estimated measurements possible to try and figure it out.
So we're talking big-ass, Balerion, Vhagar level dragons. So I'm going to use the average weight of a blue whale- 140,000kg.
80% of that is 112,000kg.
112,000kg divided by the average weight of a sheep (75.5kg) = 1483.44 (round that up to 1484).
???thats??? a lot ???of sheep??
But okay, lets assume that Balerion survived on a tasty diet of elephant.
112,000kg divided by the average weight of a elephant (6000kg) = 18.6 (round up to 19).
Okay. So either Balerion ate an absolute shit ton of sheep, or he took some nice monthly trips to the Westeros version of Africa and cut down on the elephant population.
(I mean or maybe they dont have the same metabolism of a komodo dragon or my math is wrong but I worked hard on this okay leave me alone.)
IN SUMMARY/ TL;DR :
If dragons had similar metabolism to komodo dragons:
Hatchlings would eat roughly 194 mice, or a very small fraction (0.46%) of a sheep per month.
Adolescents would eat roughly 64 sheep per month.
And giganticor dragons like Balerion and Vhagar would eat either 1483 sheep per month, or like 19 elephants per month (which seems?? like slightly more reasonable???)