What is a Watt?

The watt (symbol: W) is the SI derived unit of power, equal to one joule per second. A human climbing a flight of stairs is doing work at the rate of about 200 watts; a highly-trained athlete can work at up to approximately 2000 watts for brief periods. An automobile engine produces 25 000 watts (approximately 30 horsepower) while cruising. A typical household incandescent lightbulb uses 40 to 100 watts.