Conversion calculator for units of power
The unit of power in SI. Symbol, W (no period).
Power is a rate, the rate at which energy is expended or work done. The watt is defined as “the power which in one second gives rise to energy of 1 joule” (Resolution 2 of the CIPM, 1946, ratified by the Ninth CGPM in 1948). In mechanical terms, a power of 1 watt can, in 1 second, move a mass of 1 kilogram through a distance of 1 meter with such force that the kilogram's velocity at the end of the meter will be 1 meter per second greater than it was at the beginning. In an electric circuit, 1 watt is a current of 1 ampere at a pressure of 1 volt.
The watt's dimensions are joules per second, or in terms of base units only,
The watt was introduced at the Second International Congress of Electricians (Paris, 1889), where it was defined as 107 ergs per second. (The same conference introduced the joule, defining it as 107 ergs.)
The watt is named for James Watt (1736-1819), inventor of the
condensing steam engine.
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Last revised: 5 September 2003.