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Kilowatt hour
Kilowatt hour

The kilowatthour (symbol kWh,kW·h or kW h) is a derived unit of energy equal to 3.6 megajoules. If the energy is being transmitted or used at a constant rate (power) over a period of time, the total energy in kilowatthours is the power in kilowatts multiplied by the time in hours. The kilowatthour is commonly used as a billing unit for energy delivered to consumers by electric utilities.
The kilowatthour (symbolized kW⋅h as per SI) is a composite unit of energy equivalent to one kilowatt (1 kW) of power sustained for one hour.
One watt is equal to 1 J/s. One kilowatthour is 3.6 megajoules, which is the amount of energy converted if work is done at an average rate of one thousand watts for one hour.
The base unit of energy within the International System of Units (SI) is the joule. The hour is a unit of time "outside the SI", making the kilowatthour a nonSI unit of energy. The kilowatthour is not listed among the nonSI units accepted by the BIPM for use with the SI, although the hour, from which the kilowatthour is derived, is.
An electric heater rated at 1000 watts (1 kilowatt), operating for one hour uses one kilowatthour (equivalent to 3.6 megajoules) of energy. A television rated at 100 watts operating for 10 hours continuously uses one kilowatthour. A 40watt light bulb operating continuously for 25 hours uses one kilowatthour.
Electrical energy is sold in kilowatthours; cost of running equipment is the product of power in kilowatts multiplied by running time in hours and price per kilowatthour. The unit price of electricity may depend upon the rate of consumption and the time of day. Industrial users may also have extra charges according to their peak usage and the power factor.
The symbol "kWh" is commonly used in commercial, educational, scientific and media publications, and is the usual practice in electrical power engineering.
joule watthour kilowatthour electronvolt calorie 1 J = 1 kg·m^{2} s^{−2} = 1 2.77778 × 10^{−4} 2.77778 × 10^{−7} 6.241 × 10^{18} 0.239 1 W·h = 3.6 × 10^{3} 1 0.001 2.247 × 10^{22} 859.8 1 kW·h = 3.6 × 10^{6} 1,000 1 2.247 × 10^{25} 8.598 × 10^{5} 1 eV = 1.602 × 10^{−19} 4.45 × 10^{−23} 4.45 × 10^{−26} 1 3.827 × 10^{−20} 1 cal = 4.1868 1.163 × 10^{−3} 1.163 × 10^{−6} 2.613 × 10^{19} 1 SI multiples for watthour (W·h) Submultiples Multiples Value Symbol Name Value Symbol Name 10^{−3} mW·h milliwatthour 10^{3} kW·h kilowatthour 10^{−6} µW·h microwatthour 10^{6} MW·h megawatthour 10^{9} GW·h gigawatthour 10^{12} TW·h terawatthour 10^{15} PW·h petawatthour
 "kW h" is less commonly used. It is consistent with SI standards (but note that the kilowatthour is a nonSI unit). The international standard for SI states that in forming a compound unit symbol, "Multiplication must be indicated by a space or a halfhigh (centered) dot (·), since otherwise some prefixes could be misinterpreted as a unit symbol" (i.e., kW h or kW·h). This is supported by a voluntary standard issued jointly by an international (IEEE) and national (ASTM) organization. However, at least one major usage guide and the IEEE/ASTM standard allow "kWh" (but do not mention other multiples of the watthour). One guide published by NIST specifically recommends avoiding "kWh" "to avoid possible confusion".
 "kW·h" is, like "kW h", preferred with SI standards, but it is very rarely used in practice.
 The US official fueleconomy window sticker for electric vehicles uses the abbreviation "kWhrs".
 Variations in capitalization are sometimes seen: KWh, KWH, kwh, etc. these are inconsistent with International System of Units.
 The notation "kW/h", as a symbol for kilowatthour, is not correct.


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Kilowatt hour