Lectures on Physics has been derived from Benjamin Crowell's Light and Matter series of free introductory textbooks on physics. See the editorial for more information....

Human wattage

A typical person consumes 2000 kcal of food in a day, and converts nearly all of that directly to heat. Compare the person's heat output to the rate of energy consumption of a 100-watt lightbulb.

Looking up the conversion factor from calories to joules, we find

for our daily energy consumption. Converting the time interval likewise into mks,

Dividing, we find that our power dissipated as heat is 90 J/s = 90 W, about the same as a lightbulb.

Last Update: 2009-06-21