Assuming a mage individual has a specific organ or a system (like neural?) that can influence outside material world but in order to do so requires the energy directly fed to the cells in the same manner the muscle and neuron cells do. Meanning that it would only accept ATP or creatine phosphate (CP) and not unrefined glucose, glycogen or fats.

How much energy in joules would be available for such individual to perform an act of magic

  1. in a burst - fraction or couple of seconds.

  2. short time - tens of seconds to couple of minutes.

  3. long period - one or several hours.

  4. Through out the day.

2 - 4 meaning how much energy is available per given time value(second, minute, hour) for said period.

Quick google search says there's only around 5 Kcal worth of energy in ATP/CP on average in the body which equals to mere 20900 joules. Note that rapidly depleting most of it will result in death which implies that a person must have a surplus of it to use in the act of magic. The rest is gradually converted from glucose and glycogen.

There's a lot of similar threads but the answers tend to get carried away into total energy capacity via fat or total energy available through out the day being expended in a single act.

Things to consider:

  1. Conversion speed between ATP/CP, glucose and glycogen.
  2. Waste and other byproducts of said reactions like creatinin.
  3. ATP/CP is either evenly distributed through out body or concentrated in the certain parts of it meaning that the net(gross) value may or may not be used fully for the act.

Side questions:

  1. what constitution a mage should be to have more energy capacity?

  2. Things about diet and possibility of mana potions - something that can quickly add energy(edible glucose) or accelerate the conversion of fat/glycogen(coffeine, creatin or l-carnitine).

  3. What could be achieved with the resulting amount of energy assuming a given amount of efficiency(%) - ie it's unlikely that a mage can simply add up energy freely to someone's brain in order to fry it. There has to be a mechanism of transferring said energy which inevitably introduces waste.

  • 1
    $\begingroup$ not a direct answer, but when you are trying to affect something you could also use the energy in the environment... so a mage could use the energy of the person they are trying to hurt/affect in addition to what is available in their own bodies, or this could be by drawing in heat from the surrounding environment $\endgroup$
    – Chris J
    Aug 11, 2016 at 8:02
  • $\begingroup$ Yeah that's basicaly how most of the magic systems seem to work(Mana/Source/Force etc). But this one is the assumption of that a specific internal system is responsible for causing the desired "magical" effects on the outside world. In case this system has to be internally fed like all the other organs in an organism I ask how potent in fact it could be. $\endgroup$
    – Nick Dzink
    Aug 11, 2016 at 9:24
  • $\begingroup$ I'm guessing the answer will be <small> so then it's a case of getting the most bang for you buck... instead of throwing a fireball, you activate the nervous system of the other person $\endgroup$
    – Chris J
    Aug 11, 2016 at 9:28
  • $\begingroup$ Excellent question Nick. Welcome to the site. For more info on the site, check out the help center and feel free to join us in Worldbuilding Chat $\endgroup$
    – James
    Aug 11, 2016 at 15:48

2 Answers 2


We could play theorycraft all day long about how energy is transported among the body, chemistry, mythocondria etc. with a scientific approach to the question.

I suggest an engineering approach instead. Pick something in the body which is easy to evaluate and work from there.

Let's start with legs. Why? Because you can easily find energy expenditure tables and calculators for walking, and they are the parts that tire out in this exercise. In running you use more body parts, so I am skipping that.

A quick googling for how much percentage of the body weight a single leg represents gives us figures ranging from 10% to 16%. Assuming 10% then, if your magical organ or tissue takes 10% of your mage's body mass, you could have it produce about 60 to 160 calories per hour (the figures in the link I provided, for walking, approximately divided by two since the figures are the expenditure of two legs) in a comfortable manner for a range of time from minutes to hours before the mage tires out. That's approximately 0.07 to 0.19 kwh.

If you want to sacrifice your magical organ (an probably your life) for a lot of energy in a single instant, you could use XKCD's Zippo Phone article for a basis:

An adult man's hand weighs about a pound. The hand isn't the fattiest part of the body, but if burned completely, it would probably give off about 500 watt-hours of energy, give or take. That's 50 times the energy content of the phone battery, and almost 10 times that of the Zippo. It's also about as much as a car battery.

And, for that matter, about as much as a sandwich.

That's for the weight of a hand. If it weighted as much as a leg, supposing the same fat content of a hand, it could give almost 16 times that, about eight thousand kwh in a flash.

You can then work on your magical organ expenditure and fatigue sensation from those figures.

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    $\begingroup$ This one's more helpfull $\endgroup$
    – Nick Dzink
    Aug 11, 2016 at 11:07

Well, considering the magic comes form a certain organ and uses the same energy source as other organs it is then provided with the same powerbank. Basically it the energy you require per day. Wikipedia has the article about the average daily consumption. There are numerous calorie calculators, like this one.

It is said that if you do nothing, you need about 2000 calories, if you're engaging in serious physical activity you can consume about 4000. So it is probably reasonable to assume that instead of heavy lifting you could divert same 4000-2000=2000 calories to performing astral manipulations.

2000 calories is, well, by definition, enough energy to warm up 2000 kg of water by 1 degree Celsius, or take- 20 kilograms of water to boiling point. The microwave oven efficiency is about 60%, if mage is as sophisticated he'd be able to boil maybe a dozen kilogramm of brains before passing out from exhausting.

That being said, the impact of the human on the world is not directly linked to the energy stored inside his body. You know, buldoser driver moves mountains without breaking a sweat, a dam builder changes the direction of movement of billions of tons of water. Thus how much your mage can do is still defined by specifics of your universe: whether mage can manipulate magic in such a way to store some energy somewhere in the astral, or whether one can create magical constructs that functioon in magic like machines in physical world. And of course it heavily depends on how that magic affects physical world, if all that your glan is capable of emitting is limited to four fundamental physical fields it is one case, if it allows for a fine manipulation of fundamental particles, it is completelly different.

  • $\begingroup$ That's a shallow answer similar to the ones given in other threads and answers only a part of it. The question focuses on the burst possible output: meaning that even if I have spare 2000 Kcal per day does not mean I can exert them effeciently(fast) enough to fry someone's brain as natural heat dissipation will negate this. Also count in waste that will be produced while converting materials and it may be that the mage himself will pass out due to intoxication long before he achieves the goal. $\endgroup$
    – Nick Dzink
    Aug 11, 2016 at 10:52
  • $\begingroup$ @NickDzink Well, those are the questions YOU should answer. They are inherently linked to how your organ functions. The domain of possibilities here is infinitissimal. If you expect a robust approach based on physics, here's the answer: in a physics guided world human and other beings have 0 joules of magical energy. $\endgroup$
    – Timmy
    Aug 12, 2016 at 10:30
  • $\begingroup$ @NickDzink, that being said, if muscless are taken as reference, it is entirely possible to use them to pump energy into something up to the point of ignition. $\endgroup$
    – Timmy
    Aug 12, 2016 at 10:31

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