The watt (symbol: W) is a derived unit of power in the International System of Units (SI). It measures rate of energy conversion. One watt is equivalent to 1 joule (J) of energy per second. In terms of mechanical energy, one watt is the rate at which work is done when an object is moved at a speed of one meter per second against a force of one newton. » = = = By the definitions of electric potential (volt) and current (ampere), work is done at a rate of one watt when one ampere flo… (More on Gigawatt)