What is a Watt?

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What’s a watt and what it’s not

The watt is named after James Watt (1736–1819), who made major contributions to the development of the steam engine. A watt is actually a very small amount of electricity. To put things in perspective, the average household light requires 60 watts of electricity to operate (energy-efficient compact fluorescent bulbs average only 18 watts). The average microwave oven uses 1,500 watts. An electric oven can require as much as 5,000 watts or more to operate.

Because most appliances require thousands of watts of electricity, the more commonly used unit is the kilowatt (kw). A kilowatt is equal to 1,000 watts. The watt and its variants are also used to measure the capacity, or generating potential, of devices that make electricity. For example, the average residential solar photovoltaic (PV) system contains a capacity of about 2 to 3 kw. The capacity of larger systems, such as coal and nuclear plants, is measured in megawatts (1 mw = 1,000,000 watts) and gigawatts (1 gw = 1,000,000,000 watts).

A common error among consumers is to mistake the kilowatt with its energy usage counterpart, the kilowatt-hour (kwh). A kilowatt-hour is a measurement of electricity generated or consumed over one hour. For example, a 60-watt light bulb will consume 60 watt-hours over the course of an hour. If the bulb is used 4 hours each day for 30 days, the resulting usage will be 60 watt-hours x 4 hours x 30 days, or 7.2 kwh (7,200 watt-hours).

It’s easy to see kilowatt-hours in action. Simply take a look at your electric utility meter, typically located on the side of your home, to see a running tally of the kwh being used. The difference between the kwh recorded at beginning of the billing cycle to the end is the number that appears on your electric bill each month. That number will vary from month to month, based on the seasonal electrical demands of the dwelling. A 2,000-square-foot home typically uses around 1,000 kwh of electricity per month.