A kilowatt hour is the typical way that electricity is measured. A kilowatt (kW) is 1,000 watts, and a kilowatt hour refers to the use of a device or a set of devices that use 1,000 watts for an hour. Therefore, using a 100 watt light-bulb for 10 hours would equate to 1 kilowatt hour, as would the use of a 10,000 watt machine for 6 minutes.

Electric utilities typically charge their customers by the kilowatt hour, and the rate tends to fluctuate over time, and it also varies dramatically by region. In the United States for example, the average residential cost of a kilowatt hour in Washington is 5.7 cents and goes all the way up to 16.34 cents in Hawaii. Here are the costs per kilowatt hour by region of the United States in 2001:

region	average residential cost of a kilowatt hour
U.S. average	8.62
Pacific Noncontiguous	14.64
New England	11.94
Middle Atlantic	11.45
Pacific Contiguous	10.03
West South Central	8.45
East North Central	8.13
South Atlantic	8.05
Mountain	7.80
West North Central	7.37
East South Central	6.51

Region Definitions:

• Pacific Noncontiguous: Alaska, Hawaii
• New England: Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island, Vermont
• Middle Atlantic: New Jersey, New York, Pennsylvania
• Pacific Contiguous: California, Oregon, Washington
• West South Central: Arkansas, Louisiana, Oklahoma, Texas
• East North Central: Illinois, Indiana, Michigan, Ohio, Wisconsin
• South Atlantic: Delaware, District of Columbia, Florida, Georgia, Maryland, North Carolina, South Carolina, Virginia, West Virginia
• Mountain: Arizona, Colorado, Idaho, Montana, Nevada, New Mexico, Utah, Wyoming
• West North Central: Iowa, Kansas, Minnesota, Missouri, Nebraska, North Dakota, South Dakota
• East South Central: Alabama, Kentucky, Mississippi, Tennessee