Watt

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(Redirected from KW)

For other uses of "Watt", see Watt (disambiguation).

The watt (symbol: W) is the SI derived unit of power.

1 Definition
2 Origin
3 SI multiples
4 Conversions
5 Derived and qualified units for power distribution
- 5.1 Kilowatt-hour, MWd
- 5.2 MWe, MWt
6 See also
7 External links

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Definition

One watt is one joule of energy per second.

1 W = 1 J/s = 1 newton meter per second = 1 kg·m²·s^-3

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Origin

The watt is named after James Watt for his contributions to the development of the steam engine, and was adopted by the Second Congress of the British Association for the Advancement of Science in 1889 and by the 11th Conférence Générale des Poids et Mesures in 1960.

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SI multiples

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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Conversions

1 watt ≈ 3.412141630 BTU/h
1 watt = 1 volt × 1 ampere
1 horsepower ≈ 745.700 W (rounded up from 745.69987158227022 W)
1 horsepower (electrical British) = 746 W
1 horsepower (electrical European) = 736 W
1 horsepower ("metric") = 735.498 75 W

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Derived and qualified units for power distribution

A watt is a unit of power or the amount of energy per unit time.

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Kilowatt-hour, MWd

When paired with a unit of time the term watt is used for expressing energy consumption. For example, a kilowatt hour, is the amount of energy expended by a one kilowatt device over the course of one hour; it equals 3.6 megajoules (1 hour = 3600 seconds). A megawatt day (MWd or MW·d) is equal to 86.4 GJ (1 day = 86400 seconds). These units are often used in the context of power plants and home energy bills.

For the use of watts as a measurement of transmitter power in radio, see effective radiated power and nominal power.

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MWe, MWt

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). This is a term that refers to thermal power produced. SI prefixes can be used, for example megawatt thermal (MWt) and gigawatt thermal (GWt). For example, a nuclear power plant might use a fission reactor to generate heat (thermal output) which creates steam to drive a turbine to generate electricity. See nuclear proliferation for discussion of a reactor that generates 200 MWt (50 MWe), and another reactor that generates 800 MWt (200 MWe).

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