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# Watt

This article has been reviewed by the following Topic Editor: Tom Lawrence

SI multiples of watt
Multiple Name Symbol Multiple Name Symbol
100 watt w
101 decawatt daw 10–1 deciwatt dw
102 hectowatt hw 10–2 centiwatt cw
103 kilowatt kw 10–3 milliwatt mw
106 megawatt Mw 10–6 microwatt µw
109 gigawatt Gw 10–9 nanowatt nw
1012 terawatt Tw 10–12 picowatt pw
1015 petawatt Pw 10–15 femtowatt fw
1018 exawatt Ew 10–18 attowatt aw
1021 zettawatt Zw 10–21 zeptowatt zw
1024 yottawatt Yw 10–24 yoctowatt yw
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## Definition

<p>The watt (symbol: W) is the SI unit of power defined as one joule of energy transferred or dissipated in one second (J/s). Its expression in terms of SI base units is m2·kg·s-3. </p><p>The watt is a common unit of electrical power, in which case one watt of power is expended when one ampere of direct current flows through a resistance of one ohm. Watt electrical (abbreviation: We) is a term that refers to power produced as electricity. SI prefixes can be used, for example megawatt electrical (MWe) and gigawatt electrical (GWe). Watt thermal (abbreviation: Wt or Wth) refers to thermal power produced; again SI prefixes can be used, for example megawatt thermal (MWt) and gigawatt thermal (GWt). </p><p>For perspective, the approximate heat dissipation from an adult human is around 100 Wt. A typical kitchen microwave will be rated around 1000 W (1 kW) and a typical automobile's power output rating will be around 150 kW. </p>

## History

<p>The unit is named for James Watt (1736-1819), the Scottish inventor, instrument maker and mechanical engineer, renowned for his improvements on the steam engine. </p>

## Conversions

<p>1 watt = 1 joule/second
1 watt = 1 volt ampere
1 watt = 1·107 ergs/second
1 watt = 2.39006·10-4 kilocalorie (thermal)/second
1 watt = 9.48452·10-4 Btu (thermal)/second
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## Citation

Cutler J. Cleveland (Lead Author);Tom Lawrence (Topic Editor) "Watt". In: Encyclopedia of Earth. Eds. Cutler J. Cleveland (Washington, D.C.: Environmental Information Coalition, National Council for Science and the Environment). [First published in the Encyclopedia of Earth October 8, 2007; Last revised Date October 8, 2007; Retrieved May 25, 2013 <http://www.eoearth.org/article/Watt>

## The Author

Cutler J. Cleveland  is Professor of Earth and Environment at Boston University, where he also is on the faculty of the Center for Energy and Environmental Studies. Professor Cleveland is Editor-in-Chief of the Encyclopedia of Energy (Elsevier, 2004), winner of an American Library Association award, the Dictionary of Energy (Elsevier, 2005), Handbook of Energy (Elsevier, forthcoming), and is the Founding Editor-in-Chief of the Encyclopedia of Earth.  He is the recipient of the Adelma ... (Full Bio)