If you’re like me and you’ve always wished that Pokémon were real, no doubt you’ve dreamt of having one of your very own as a pet. I don’t really like pets, they look like a lot of effort and stop you doing fun things like going on holiday, but if I could have a Charizard living in my backyard, well now that’s a whole new ball game…

Let’s suppose that is exactly the case – you have a pet Charizard living in your garden. For those of you unfamiliar with Charizard, think fire-breathing dragon and you’ve pretty much nailed it. As with all pets (I assume) you have to think about how much food to feed them, or more specifically how many calories does your pet need in order to survive. An average sized dog needs around 800 calories per day, whilst cats are a little smaller and so only need about 300. So as with most things in life, size matters, which brings us back to our fire-breathing dragon…

Game of Thrones fans a word of warning: dragons aren’t all as big as the ones belonging to Daenerys. The main one Drogon is often pictured as being at least ten metres tall and weighing as much as a small house, but that is not the case with Charizard. Pokémon tend to be much smaller than you might think and according to the official Pokédex an average Charizard stands at 1.7 metres tall and weighs in at 90 kilograms. I don’t know if this was on purpose but that is almost exactly the same as the average height and weight for a male human. The recommended daily intake of calories for such a male is 2500 per day, which gives us a good starting point for our pet Charizard. But, we also need to think about fire.

A fire needs three key ingredients to burn successfully: fuel, heat and oxygen (see fire triangle above). If any of the three are missing, then the fire will go out (this is why it’s called the ‘fire triangle’, as without one of its sides a triangle is no longer a shape). Charizard has a flame burning on its tail that is said to grow hotter with increased battle experience. We can safely assume that the tail flame is getting its supply of oxygen from the atmosphere, which contains 21% of the gas. The majority (78%) of the air is nitrogen plus a few other bits and pieces such as unreactive argon (0.93%) and the big baddie carbon dioxide at what seems a measly 0.04%, but is still enough to heat up our planet.

That’s the oxygen taken care of, now what about the heat? Well Charizard is probably quite a warm creature, especially with all of this fire-breathing going on, so it’s probably safe to say that the heat comes from its body. That just leaves the fuel – it has to burn something to be able to produce fire. The most likely culprit is to burn its food, i.e. calories. A calorie by definition is approximately the amount of energy required to raise the temperature of one gram of water by one degree Celsius at a pressure of one atmosphere. Just to be super confusing, the calories we talk about with food are actually kilogram calories and are equal to 1000 of the little ones. This is why calorie content on food labels is often given in both units of kcal and cal, though not always (again just to be super confusing).

If we assume that the flame on Charizard’s tail burns similar to a lab Bunsen burner (a reasonable assumption I feel), then it will generate a power of around 1 kilowatt. Therefore, in order to burn for 24 hours, it requires 24 kilowatt hours of energy – a kilowatt hour is just the amount of power in kilowatts times the length of time it is produced for in hours. We know that 1 food calorie is equal to 0.00162 kilowatt hours (thanks Wikipedia) and so the number of calories required to power the flame on the tail of a Charizard is

Just to clarify this is the big food-based calorie, which means a LOT of food for your fire-breathing pet dragon. Even with a conservative estimate, a Charizard is going to need to eat as much food as 6 fully grown men to be able to keep it active for just one day. Maybe I was right and pets aren’t such a good idea after all – especially the ones that breathe fire…

All of the material in the Pokemaths series can be found here.