A kilowatt is a measure of power while a kilowatt-hour is a measure of energy. One kilowatt equals 1,000 watts and one kilowatt-hour is equivalent to 3.6 million joules of energy. Kilowatts measure energy usage and generation while kilowatt-hours measure the amount of fuel contained within something or consumed over a set period of time.
The watt is the derived unit of power recognized by the International System of Units. Watts express the rate of energy transfer or conversion with respect to time. The kilowatt is typically used to express the power output of engines, electric motors, machines, heaters and tools. One kilowatt is roughly equal to 1.34 horsepower.
The total energy in a kilowatt-hour is found by multiplying the power in kilowatts by the time in hours. The kilowatt-hour is typically used as a billing unit by electric companies to determine the energy consumption of a consumer. While electrical energy is sold to consumers in kilowatt-hours, the unit price of electricity may also be dependant upon the rate of consumption and time of day. Major electricity production or consumption is often measured in terawatt-hours. Even larger units such as the terawatt-hour and petawatt-hour can express the annual electrically generated or consumed by whole countries.