kWh meters are compact electronic monitoring devices that measure the consumed energy flowing through a circuit such as a standard 120V or 240Vac line and act as a kWh calculator. The meter is mounted in line with the circuit supplying the electricity such as a main panel or distribution sub panel and will accumulate a totalized reading accounting for the consumption flowing through. The accumulated number is the total power in kilowatts that has been used over a period of time, thus giving you the energy as expressed in kilowatt hour.