# Kilowatt Hour Meters

## What is Kilowatt Hour (kWh) Metering?

The kilowatt-hour (SI symbol: kW⋅h or kW h; commonly written as kWh) is a unit of energy equal to one kilowatt of power sustained for one hour and is commonly used as a measure of electrical energy. One kilowatt-hour is equal to 3600 kilojoules (3.6 megajoules). The kilowatt-hour is a composite unit of energy equal to one kilowatt (kW) times one hour. Expressed in the standard unit of energy in the International System of Units (SI), the joule (symbol J), it is equal to 3600 kilojoules (3.6 MJ).[1][2].

The hour is a unit of time listed among the non-SI units accepted by the International Bureau of Weights and Measures for use with the SI.[3] Its combination with the kilowatt, a standard SI unit, is therefore permitted within the standard.

A widely used representation of the kilowatt-hour is "kWh", derived from its component units, kilowatt and hour. It is commonly used in billing for delivered energy to consumers by electric utilities and in commercial, educational, and scientific publications and in the media.[4][5] It is also the usual unit representation in electrical power engineering.[6] This common representation, however, does not comply with the style guide of the International System of Units (SI).[3]. Other representations of the unit may be encountered:. "kW⋅h" and "kW h" are less commonly used, but they are consistent with the SI. The SI brochure[3] states that in forming a compound unit symbol, "Multiplication must be indicated by a space or a half-high (centred) dot (⋅), since otherwise some prefixes could be misinterpreted as a unit symbol."

This is supported by a voluntary standard[7] issued jointly by an international (IEEE) and national (ASTM) organization, and by a major style guide.[8] However, the IEEE/ASTM standard allows "kWh" (but does not mention other multiples of the watt-hour). One guide published by NIST specifically recommends against "kWh" "to avoid possible confusion".[9]. The United States official fuel-economy window sticker for electric vehicles uses the abbreviation "kW-hrs".[10]. Variations in capitalization are sometimes encountered: KWh, KWH, kwh, etc., which are inconsistent with the International System of Units.

## Kilowatt Hour (kWh) Metering Frequently Asked Questions

The notation "kW/h" for the kilowatt-hour is incorrect, as it denotes kilowatt per hour.

- Electrical energy is typically sold to consumers in kilowatt-hours.
- The cost of running an electrical device is calculated by multiplying the device's power consumption in kilowatts by the operating time in hours, and by the price per kilowatt-hour.
- The unit price of electricity charged by utility companies may depend on the customer's consumption profile over time. Prices vary considerably by locality. In the United States prices in different states can vary by a factor of three.[11]. While smaller customer loads are usually billed only for energy, transmission services, and the rated capacity, larger consumers also pay for peak power consumption, the greatest power recorded in a fairly short time, such as 15 minutes.

This compensates the power company for maintaining the infrastructure needed to provide peak power.

These charges are billed as demand changes.[12] Industrial users may also have extra charges according to the power factor of their load. Major energy production or consumption is often expressed as terawatt-hours (TWh) for a given period that is often a calendar year or financial year.

A 365-day year equals 8,760 hours, so over a period of one year, power of one gigawatt equates to 8.76 terawatt-hours of energy.

Conversely, one terawatt-hour is equal to a sustained power of about 114 megawatts for a period of one year.

An electric heater consuming 1000 watts (1 kilowatt), and operating for one hour uses one kilowatt-hour of energy.

A television consuming 100 watts operating continuously for 10 hours uses one kilowatt-hour. A 40-watt electric appliance operating continuously for 25 hours uses one kilowatt-hour.

In terms of human power, a healthy adult male manual laborer performs work equal to about half a kilowatt-hour over an eight-hour day.[13].

To convert a quantity measured in a unit in the left column to the units in the top row, multiply by the factor in the cell where the row and column intersect.

All the SI prefixes are commonly applied to the watt-hour: a kilowatt-hour is 1,000 Wh (kWh); a megawatt-hour is 1 million Wh (MWh); a milliwatt-hour is 1/1000 Wh (mWh) and so on.The kilowatt-hour is commonly used by electrical energy providers for purposes of billing, since the monthly energy consumption of a typical residential customer ranges from a few hundred to a few thousand kilowatt-hours.