If you leave a device plugged in, it'll use a little of energy, 1-5 watts, and takes 200 to 1k hrs to use a KW hour, costing 10¢.
Electric power is the rate at which electric energy is transferred by an electric circuit. The SI unit of power is the watt, one joule per second.
Electric power is usually produced by electric generators, but can also be supplied by chemical sources such as electric batteries. Electric power is generally supplied to businesses and homes by the electric power industry. Electric power is usually sold by the kilowatt hour (3.6 MJ) which is the product of power in kilowatts multiplied by running time in hours. Electric utilities measure power using an electricity meter, which keeps a running total of the electric energy delivered to a customer. Measurement
The kilowatt hour, or kilowatt-hour, (symbol kW·h, kW h or kWh) is a unit of energy equal to 1000 watt-hours or 3.6 megajoules. For constant power, energy in watt-hours is the product of power in watts and time in hours. The kilowatt-hour is most commonly known as a billing unit for energy delivered to consumers by electric utilities.
The kilowatt-hour (symbolized kWh) is a unit of energy equivalent to one kilowatt (1 kW) of power expended for one hour. Technology Internet