The watt is the rate a source of energy uses or produces one joule during one second, so the same quantity may be referred to as a joule per second, with the symbol J/s. It can also be written as kg·m2·s−3.
1000 watts is called a kilowatt, written as kW. In many countries, electric bills are based on how many kilowatt-hours are being used.
1000000 watts is called a megawatt, written as MW. This is used to describe how much electricity is needed by a large town.