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: W_e) is a term that refers to power produced as electricity. SI prefixes can be used, for example megawatt electrical (MW_e) and gigawatt electrical (GW_e). Watt thermal (abbreviation: W_t or W_th) refers to thermal power produced; again SI prefixes can be used, for example megawatt thermal (MW_t) and gigawatt thermal (GW_t). </p><p>For perspective, the approximate heat dissipation from an adult human is around 100 W_t. 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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Further Reading

• How Many? A Dictionary of Units of Measurement, Russ Rowlett, Center for Mathematics and Science Education, University of North Carolina at Chapel Hill
• SI base units and SI derived units, the Physics Laboratory, National Institute of Standards and Technology
• Energy conversion tool at unitconversion.org.