The kilowatt (kW) equals 1,000 watts and is the standard unit for measuring the power output of engines, electric heaters, and industrial machinery. Electricity bills use kilowatt-hours (kW × hours), making the kilowatt the most familiar power unit for consumers. One kilowatt equals approximately 1.341 horsepower.

BTU per hour (BTU/h) equals approximately 0.293 watts, the standard rating unit for air conditioners, heaters, and furnaces in North America. A typical window air conditioner rated at 10,000 BTU/h can cool a 400–500 square foot room, making this unit essential for HVAC system sizing. One BTU/h equals about 0.2931 watts.