unit of power in the International System of Units (SI) equal to one joule of work performed per second, or to ¹/₇₄₆ horsepower. An equivalent is the power dissipated in an electrical conductor carrying one ampere current between points at one volt potential difference. It is named in honour of James Watt (Watt, James), British engineer and inventor. One thousand watts equal one kilowatt. Most electrical devices are rated in watts.