Human energy consumption: How dim is your lightbulb?

Ever looked at your electricity bill and wondered "gee, how many kilowatt hours does my body use?" Wonder no longer. Here's how to figure it out.

An adult body needs, on average, 12 kilocalories per pound to maintain it's weight. If you want to add a pound of fat, you need an extra 3600 kilocalories. My "ideal weight" for my height according to most charts I've looked at is 195 pounds. So, my body needs 12 x 195 lbs = 2,340 kilocalories to maintain it's weight. Now lets convert that to watts.

2,340 kilocalories per day / 24 hours = 97.5 kilocalories per hour / 3600 seconds per hour = 0.0271 kilocalories per second x 4,184 joules / kilocalorie = 113.32 joules/second or 113.32 watts. So I'm roughly equal to the power consumption of a slightly bright light bulb (100 watts is a little above average).

If I draw 113.32 watts for an entire hour, that's .113 kilowatt hours. Over a 24 hour span, that's 2.712 kilowatt hours per day. Over an entire year, that's 989.88 kilowatt hours. At an average price of say, $0.11 per kilowatt hour for electricity - that means my body would consume $108.89 of electricity per year if I could somehow plug myself into the wall.

Interestingly, the brain is on average 2% of the body's mass but consumes 20% of the body's energy. In my case, my brain should weigh 3.9 lbs and uses 197.97 kilowatts of energy per year.

The actual power output of the human body is MUCH lower than the amount of energy it consumes. A human being can put out something like 100 watts of power on average (say, by driving a stationary bicycle) over a long span of time. Lets look at the maximum efficiency of a human.

150 lbs = 87 watts = 2.1 kilowatt hours per day energy consumed
100 watts per hour x 10 hours a day = 1 kilowatt hour

1.0 / 2.1 = 47.6% efficient

A horse is supposedly about 8 times more powerful than a human. That's why 1 horsepower is equal to 745.7 watts. Consider how incredibly powerful your car is: my car has 173 horsepower at peak at the crank. To the wheels, on average, it probably puts down something like 65 horsepower or 48,740 watts of power. In other words, I would have to work 487 seconds (8 minutes) to equal the power output of 1 second on average from my car.