A kilowatt-hour (kWh) is a unit of energy that is commonly used to measure electricity consumption. It is the equivalent of one kilowatt (1 kW) of power expended for one hour of time. For instance, if you have a 1 kW device, like an electric heater, running it for one hour would consume 1 kWh of energy. If the device was 100 watts, like a light bulb, you would need to run it for ten hours to consume 1 kWh of energy. In terms of billing, electricity companies use kWh to calculate how much to charge on your electricity bill. The more kWh you've used during a billing period, the higher your bill will be. This unit allows for a simple way to understand and track energy usage over time.