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Differing characteristics of electricity are measured in different ways. Volts and amperes (“amps”) are measures of electrical voltage and current. A common analogy compares electricity flowing through a wire with water flowing through a pipe. The current (amps) is the amount of water that is flowing, while the voltage (volts) represents the pressure on the water that is making it flow.

Power is the source or means of supplying energy. The measurement of electrical power is the measurement of the amount of work done by electrical energy. A common measure of power is horsepower, but electrical power is usually measured in Watts.

Electric Service Meter  © 2012 Consumers Energy

The true measure of power as work includes the time factor. For instance, a 100 Watt light bulb, burning for 1 hour, will consume 100 Watt-hours (Wh) of electrical power. Ten of these 100 Watt bulbs burning for one hour (or one bulb burning for ten hours) will use 1,000 Watt-hours, or 1 kiloWatt-hour (kWh).

For most purposes, the energy used in buildings by electrical power is measured in kWh. This is how electricity is bought and sold.

Remember, a Watt (or kiloWatt) is an instantaneous measure of the level of power being expended at any one time, and a Watt-hour (or kiloWatt-hour) is a measure of the amount of energy expended over time. A useful analogy is the speedometer and odometer in an automobile. The “speedometer” could be marked in kW (how fast they are being used), and the odometer would show kWh (how many were used at the end of the trip). Much as electricity is sold by the utility to the consumer, an automobile rental is based on the total mileage driven, and not the top speed!