What is a watt?

The watt is named after Scottish engineer James Watt, whose improvements to the steam engine helped drive the Industrial Revolution. A 10-watt LED bulb uses 10 joules of energy every second. Electricity bills measure energy in kilowatt-hours: running a 1,000-watt appliance for one hour uses 1 kWh. Watt himself coined the term horsepower, and one mechanical horsepower equals about 746 watts. A resting human body gives off roughly 100 watts of heat, similar to an old incandescent bulb.