# How many watts does the human body use

#### Chaos' lil bro Order

how many watts does the human body use

i guess 500w

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how many watts does the human body use

i guess 500w
I once read, in connection with crew in a space habitat, that an adult human radiates like a 100 watt light bulb. You could figure the other from that, assuming eqquilibrium. Your guess looks to be in the ball park.

#### jim mcnamara

Mentor
You can work it out from knowing kCal of food metabolized that results in equilibrium - it's called basal metabolic rate (BMR). It's the rate of oxygen consumption (or CO2 production) per Kg of body weight when the bodyy is at rest.

play with this applet:
http://www.bmi-calculator.net/bmr-calculator/

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You can work it out from knowing kCal of food metabolized that results in equilibrium - it's called basal metabolic rate (BMR). It's the rate of oxygen consumption (or CO2 production) per Kg of body weight when the bodyy is at rest.

play with this applet:
http://www.bmi-calculator.net/bmr-calculator/
Hey thanks for that. I got my BMR to be 1554 (ignoring the decimals) which is a number I have been trying tofind.

#### Chaos' lil bro Order

My BMR is 1888, so what's that mean my wattage is?

#### jim mcnamara

Mentor
Watts measure power, Kcal measures energy. If you're willing to go with Watt-hours to get everything in the same units of measure:

1 KCal = 1.163 watt-hour, if I remember correctly.

So, 1888 * 1.163 = 2915 Watt-hours

#### Panda

The recommended UK Male Calorie intake is 2550 Calories/ Day
1 Calorie (Nutritional) = 4186.8 Joules

So assuming zero weight gain, and waste having no nutritional value you must dissipate 123.6 J/s or Watts, or the heat generated by burning 12.5oz of coal.

What the proportion of heat/motion is depends on how warm your personality is....

#### marcusl

Gold Member
My BMR is 1888, so what's that mean my wattage is?
BMR has units of power. The web site given in the link above is using kcal/day, although units aren't given there, so to convert to watts
1888 kcal/day * 4.18 kJ/kcal * 1 day / 8.64e4 sec = 91.3 Watts

BMR depends on body weight and percentage body fat, since muscles generate heat, age, sex, and other factors including individual variability.

#### tehno

Most of the energy is consumed by the brain I think .

#### Chaos' lil bro Order

Nice replies fellas.

So ~100W seems to be a good ballpark figure for a human body's power output. Funny that a 100W light bulb is on par with the human body!

SelfAdjoint says 'he heard' the brain uses 25% of this, so 25W, I wonder how true this is.

Very interesting thread so far, what else can we think of that's on topic?

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Nice replies fellas.

So ~100W seems to be a good ballpark figure for a human body's power output. Funny that a 100W light bulb is on par with the human body!

SelfAdjoint says 'he heard' the brain uses 25% of this, so 25W, I wonder how true this is.

Very interesting thread so far, what else can we think of that's on topic?
So what you could do now is reexpress your calories of food (which are really kilocalories, you know) as watt-hours, and see what your energy balance is. Or different kinds of excercise, what are their wattage requirements? Getting away from the dietician's calorie seems to be a refreshing way to think about our daily regimen.

#### marcusl

Gold Member
Nice replies fellas.

So ~100W seems to be a good ballpark figure for a human body's power output. Funny that a 100W light bulb is on par with the human body!

SelfAdjoint says 'he heard' the brain uses 25% of this, so 25W, I wonder how true this is.

Very interesting thread so far, what else can we think of that's on topic?
Years ago I visited the precision metrology lab at HP Labs, which was temperature controlled to keep the instruments, meter bars and such constant. At the entrance to the room was a panel of light switches that controlled 100W bulbs inside. Each person entering turned off 100W, and turned it back on when they left, so the heat load inside stayed approximately constant.

#### DaveC426913

Gold Member
SelfAdjoint says 'he heard' the brain uses 25% of this, so 25W, I wonder how true this is.
The brain uses 25% of the body's oxygen, so that seems about right. Unless there are anaerobic prcoesses at work in the body?

#### Chaos' lil bro Order

So what you could do now is reexpress your calories of food (which are really kilocalories, you know) as watt-hours, and see what your energy balance is. Or different kinds of excercise, what are their wattage requirements? Getting away from the dietician's calorie seems to be a refreshing way to think about our daily regimen.

I couldn't agree with you more self. Calories and kilojoules are like pints and quarts to me. I much prefer terms like eV and Watts since batteries and machines and such all label their power usages in these terms. It makes comparisons easy and much more interesting.

@Marcus
Now there's a real-life application that really solidifies and roots this thread in the practical. Its very interesting to hear your example.

#### quasi426

Look around and imagine how we remain.

We do not radiate all the energy we consume, so if we radiate like a 100 Watt light bulb we actually require a higher wattage since the human body is a very very ordered thing indeed. Just look at your eye ball in the mirror and try to imagine all the meticulous planning and processes that are occurring, the structure it possess. Now think how is all this kept ordered? Energy of course, energy input is required. So eating food is needed to keep our high entropy state going the way its going. To recap in a line: energy inputed is outputted through various radiations and is used to maintain order.

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#### marcusl

Gold Member
I couldn't agree with you more self. Calories and kilojoules are like pints and quarts to me. I much prefer terms like eV and Watts since batteries and machines and such all label their power usages in these terms. It makes comparisons easy and much more interesting.
Careful about mixing up energy and power units. In fact, the energy content of food is ubiquitously quoted in Calories, so there isn't much getting away from it. That's why treadmills and exercise bikes display the energy you have burned in units of Calories instead of joules--you can directly compare input and output.

Another commonly used unit is Mets (metabolic equivalents). 1 met is the same as your BMR; you expend about 4 mets mowing the lawn, while 12 mets is about as hard as you can exercise for any length of time. It's a useful gauge of relative effort.

@Marcus
Now there's a real-life application that really solidifies and roots this thread in the practical. Its very interesting to hear your example.
Thanks!

We do not radiate all the energy we consume, so if we radiate like a 100 Watt light bulb we actually require a higher wattage since the human body is a very very ordered thing indeed. Just look at your eye ball in the mirror and try to imagine all the meticulous planning and processes that are occurring, the structure it possess. Now think how is all this kept ordered? Energy of course, energy input is required. So eating food is needed to keep our high entropy state going the way its going. To capitulate in a line: energy inputed is outputted through various radiations and is used to maintain order.
Energy balance is conceptually pretty simple: whatever doesn't come out as mechanical work is dissipated as heat. There is some entropy content to thoughts that might be calculated by Shannon's theorem but I think it's completely negligible compared to the rest.

#### Chaos' lil bro Order

Careful about mixing up energy and power units. In fact, the energy content of food is ubiquitously quoted in Calories, so there isn't much getting away from it. That's why treadmills and exercise bikes display the energy you have burned in units of Calories instead of joules--you can directly compare input and output.

Another commonly used unit is Mets (metabolic equivalents). 1 met is the same as your BMR; you expend about 4 mets mowing the lawn, while 12 mets is about as hard as you can exercise for any length of time. It's a useful gauge of relative effort.

Thanks!

Energy balance is conceptually pretty simple: whatever doesn't come out as mechanical work is dissipated as heat. There is some entropy content to thoughts that might be calculated by Shannon's theorem but I think it's completely negligible compared to the rest.
Ya I know calories/joules are energy. Did you see I mentioned eV? Calories = joules = eV, you just need to use simple conversion formulas. Watts is power, which is simply energy/time. I'm not confusing anything here.

btw, I don't know what country you are in, but most nutritional info in Canada is in both kCal and kJ, so its not as ubiquitous as you think.

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I'm with li'l bro. If we go to Joules and Watts, people might even start to understand energy vs. power. The idea of using the same units in your regimen as you see on your electric bill might be really liberating. And I like mets too. If you could get mets ratings for different activities the way you can find the calorie rating of almost any food, you could plan so much better.

#### marcusl

Gold Member
btw, I don't know what country you are in, but most nutritional info in Canada is in both kCal and kJ, so its not as ubiquitous as you think.
That's cool! In the US food packaging gives only Calories.

I'm with li'l bro. If we go to Joules and Watts, people might even start to understand energy vs. power. The idea of using the same units in your regimen as you see on your electric bill might be really liberating. And I like mets too. If you could get mets ratings for different activities the way you can find the calorie rating of almost any food, you could plan so much better.
Charts are readily available online. See, for instance,
http://www.hsph.harvard.edu/nutritionsource/Exercise.htm" [Broken]

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#### backdoorstudent

how many watts does the human body use

i guess 500w

500 watts = 7.17 food calories (kilocalories) per minute

The average person needs between 1000-2000 food calories per day.
500 watts is about the amount of power an average person can put into the cranks of a bicycle for a few seconds. World class cyclists can deliver 500 watts to the cranks for more than 30 minutes and burn 4,000-8,000 food calories in a race.

Incidentally, 500 watts into the cranks of a standard racing bicycle will push it to a speed of about 30 mph on flat ground.

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#### marcusl

Gold Member
Wow! I guess that's why pro cyclists are always used for human powered aircraft trials.

#### Chaos' lil bro Order

I'm with li'l bro. If we go to Joules and Watts, people might even start to understand energy vs. power. The idea of using the same units in your regimen as you see on your electric bill might be really liberating. And I like mets too. If you could get mets ratings for different activities the way you can find the calorie rating of almost any food, you could plan so much better.
Ya self, I agree, MET is a good unit to put human power usage in various activities in perspective. I've never heard of it before, so I am happy to learn a new thing that will further my understanding of life.

#### bimbim

you have all overlooked something. generating power for a bike to put out 500 w. at the wheels would take a lot more overall energy. heat lost through body, body's usual working load? i recon someone generating 500 w is actually consuming about 2k. give or take a few watts. that got ya thinkin eh! here check this 'How efficient is the human body at producing power on a bike generator?

Typically the average person is able to run about 25% efficiency. This means that for every Watt produced by a bike generator, the person doing the pedaling is putting out 4 Watts. So if you are pedaling to provide to your laptop computer at 80 Watts, you body is really running at 240 Watts'.

#### mariajones

Hello Friend
Watts are not "in" the human body. Watts are a unit of power, and the human body in very good shape, can put out about 300 watts of power.
At rest a human body puts out perhaps 100 watts of power as heat.

#### bimbim

Hello Friend
Watts are not "in" the human body. Watts are a unit of power, and the human body in very good shape, can put out about 300 watts of power.
At rest a human body puts out perhaps 100 watts of power as heat.
ok on cross trainer i do 600 cals in 30 mins-can you tell me how many watts i would be using overall?
i have problems logging in here sometimes are you on facebook?

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