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I'd like to know what kind of power human body needs to maintain life, in still state (average daily power consumption of an average man is also of interest). In terms of watts.

I've only managed to find one figure - 1700 kcal per day without physical activity. That converts to 80 watts, which seems (intuitively) a bit low, so I wonder if it's the right figure or not.

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    $\begingroup$ > 1700kcal=7000kJ=a lot of ice turned into steam. Actually @Amory 7000KJ isn't going to turn that much ice into steam If you ask how much quantity of heat is required to convert 1 kg of ice into vapour then you have to add latent heat of fusion that is 336 kj/kg and latent heat of vaporization 2257 kj/kg (these two process occur at constant temperature so need to add rise in tempeature) So it will be: Q= 1×336 + 1× 4.18 ×100 + 1× 2257 Q = 3011 kj Or 3.01 Mj So you can turn ~2.33 KG ice at 0° into steam at 100° with that energy. $\endgroup$
    – Jesper
    Jan 13, 2020 at 19:11

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You're basically correct. I don't know if you've found the Wikipedia article on Basal Metabolic Rate but it's got everything you need, including a bunch of formulas you can use to figure out an average value for a given body type. There are also many online calculators, such as this one. You can easily figure out averages, which I think is what you want, but between two individuals the number can change quite a bit.

Why does 80 watts sound so low? This is more of a physics.se answer, but Watts are a unit of power which mean they measure energy use over time; W=J/s, or Joules per second. Every second. Have you ever touched a 75 watt lightbulb? They're hot as hell. If your human does nothing all day, s/he will be like an inefficient incandescent lightbulb on for a full 24 hours. Maybe that seems low but electricity is relatively cheap these days. To use another classic physics experiment, 1700kcal=7000kJ=a lot of ice turned into steam.

No wonder my father always made me turn the light off in the bathroom...

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    $\begingroup$ A bulb is exactly what I thought about. Temperature is inversely related to surface area. Body has much higher area than a bulb, so will have much lower temperature given the same power dissipated, and it has to maintain 37C. And not all power consumed by body dissipates as heat. But that's just intuition, like I said. I didn't do the math. $\endgroup$
    – Violet Giraffe
    Aug 25, 2013 at 16:45

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