What is a gigawatt-hour (GWh)?

How big is a gigawatt-hour?

Electrical power, the rate at which electricity flows at a given moment, is measured in watts. The U.S. Energy Information Administration (EIA) explains that a kilowatt is 1,000 watts, a megawatt is 1,000 kilowatts and a gigawatt is 1,000 megawatts, or one billion watts. Energy is power used over a period of time and is measured in watt-hours. One kilowatt-hour (kWh) is one kilowatt sustained for one hour, and it is the unit utilities generally use to measure electricity.

A gigawatt-hour is therefore one gigawatt sustained for one hour, which works out to 1,000 megawatt-hours or one million kilowatt-hours. For scale, the average U.S. residential utility customer bought 10,791 kWh of electricity in 2022, according to the EIA. One gigawatt-hour is about what 93 such homes buy in a year.

Gigawatts versus gigawatt-hours

The two units are easy to confuse. A gigawatt (GW) measures power: how much electricity can flow at one instant. A gigawatt-hour measures energy: the total amount delivered or stored.

A battery storage system has both ratings. The EIA describes power capacity, in watts, as the most a system can put out at once, and energy capacity, in watt-hours, as the total it can store or discharge. Utility-scale batteries in the United States had 8,842 megawatts of power capacity and 11,105 megawatt-hours of energy capacity, about 11 GWh, at the end of 2022.

Where the unit shows up

Battery makers and their customers use gigawatt-hours for three kinds of figures.

• Batteries sold. CATL reported lithium-ion battery sales of 661 GWh in 2025.
• Factory capacity. The same report put the company's global production capacity at 772 GWh in 2025.
• Storage deployed. Tesla said it deployed 13.7 GWh of energy storage products in the third quarter of 2026.

Because these figures count different things, a GWh of factory capacity is not the same as a GWh of batteries sold or installed.