A kilowatt hour is a unit of energy, and the typical way that electricity is measured. A kilowatt (kW) is 1,000 watts (w), and a kilowatt hour refers to the use of a device or a set of devices that use 1,000 watts for one hour. Using a 100 watt light-bulb for 10 hours would equal 1 kilowatt hour (kWh), as would the use of a 10,000 watt machine for 6 minutes.
Kilowatts and Kilowatt Hours
A watt or kilowatt is a measure of power, or how much electricity is being used by a device at a particular moment. This is useful information, because it can be used to compare average energy consumption; an 11 watt compact fluorescent light (CFL) bulb might produce the same amount of light as a 100 watt incandescent bulb, making it more efficient. Like knowing the average miles per gallon (or kilometers per liter) that a car gets, the devices can be compared without taking how long they are being used into account.
Energy is a measurement of power over some period of time. Power companies use the kilowatt hour because power use is cumulative. Someone who uses an 11 watt CFL isn’t paying for the 11 watts that the bulb uses in any given instant, but rather how much power is used by that bulb over a month. To determine this cost, how many kilowatts a device uses is multiplied by how many hours it is used to get kWh, which are then multiplied by the price of electricity per kWh.
watts ÷ 1,000 = kWh
kWh × hours of operation × rate = cost
Electricity Rates
Electricity prices are measured by kilowatts used in an hour, and the rate tends to fluctuate over time — both over the long-term, as in a week or month, but also over the course of a single day at the wholesale level. In some countries and regions, prices for electricity can vary based on the time of day in which the power is used; in many other places, however, prices are set by the government or based on the average cost over time. Smart meter technology and “time-of-use” pricing is expected to become more widespread over time, however.
Prices also vary dramatically by region, often based on how much it costs to generate and distribute power, as well as taxes and other charges. In the United States for example, the average residential cost of a kilowatt hour in Wyoming is 6.2 cents and goes all the way up to 25.12 cents in Hawaii.
Electricity Rates in the US
Here are the costs per kilowatt hour by region of the United States in 2010:
Region
Average Residential Cost of a Kilowatt Hour
U.S. average
9.83
Pacific Noncontiguous
19.94
New England
14.44
Middle Atlantic
13.80
South Atlantic
10.08
East North Central
9.12
Pacific Contiguous
9.07
East South Central
8.20
West South Central
8.00
Mountain
7.84
West North Central
7.80
Region Definitions:
Pacific Noncontiguous: Alaska, Hawaii
New England: Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island, Vermont
Middle Atlantic: New Jersey, New York, Pennsylvania
South Atlantic: Delaware, District of Columbia, Florida, Georgia, Maryland, North Carolina, South Carolina, Virginia, West Virginia
East North Central: Illinois, Indiana, Michigan, Ohio, Wisconsin
Pacific Contiguous: California, Oregon, Washington
East South Central: Alabama, Kentucky, Mississippi, Tennessee
West South Central: Arkansas, Louisiana, Oklahoma, Texas
Mountain: Arizona, Colorado, Idaho, Montana, Nevada, New Mexico, Utah, Wyoming
West North Central: Iowa, Kansas, Minnesota, Missouri, Nebraska, North Dakota, South Dakota