Electricity explained Measuring electricity

Electricity is measured in Watts and kilowatts

Electricity is measured in units of power called Watts, named after James Watt, the inventor of the steam engine. One Watt is a very small amount of power. Some devices need only a few Watts to operate, but other devices require larger amounts, and their consumption is measured in kilowatts (kW). One kilowatt is equal to 1,000 Watts.

For very large amounts of electricity, like what power plants generate, we use even larger units:

• Megawatts (MW): One MW is 1,000 kW, or 1,000,000 Watts.
• Gigawatts (GW): One GW is 1,000 MW, or 1,000,000,000 Watts.

Electricity use over time is measured in Watthours

Watts measure power at a specific moment, but we use Watthours (Wh) to measure how much electricity is used over a period of time. One Watthour is the energy of one Watt used for one hour.

Electric utilities and power plants generally measure electricity in kilowatthours (kWh). One kWh is one kilowatt generated for one hour. For example, if you use a 40-Watt (0.04 kW) light bulb for five hours, you have used 200 Wh, or 0.2 kWh, of electrical energy.

Utility companies measure and monitor electricity use with meters

Electric utility companies use meters to measure how much electricity their customers use. These meters are usually located on the outside of the building or home where the power line connects. In the past, electricity meters were mechanical devices that a utility employee had to read manually. Eventually, automated meters could periodically report electricity use to the utility. Today, many utilities use electronic smart meters. These meters wirelessly send power usage data in real time. Some advanced smart meters can even track the electricity use of individual devices and allow the utility or customer to control electricity use remotely.