The watt (W) is the SI base unit of power, defined as one joule per second, measuring the rate of energy transfer. From light bulb brightness ratings to phone charger output, the watt appears in everyday product specifications worldwide. One watt equals exactly 1 joule per second, or about 0.001341 horsepower.

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.