Other common units of power include kilowatts (kW), British thermal units (BTU), horsepower (hp), and tons. Watts, kilowatts and kilowatt-hours: Watts (W) is a unit of power used to quantify the rate of energy transfer. It is defined as 1 joule per second. A kilowatt is a multiple of a watt. One kilowatt (kW) is equal to 1,000 watts.