A Gigawatt-hour (GWh) is a unit of energy equal to one billion watt-hours (1,000,000,000 Wh). It is commonly used to measure the energy output of large power plants, national electricity grids, or the annual consumption of large cities.

A Megawatt-hour (MWh) is a unit of energy equal to one million watt-hours (1,000,000 Wh). It is 1,000 times smaller than a GWh and is frequently used to measure the output of wind farms, large industrial facilities, or the energy traded in wholesale markets.

To convert GWh to MWh, you multiply the number of Gigawatt-hours by 1,000. For example, 2 GWh × 1,000 = 2,000 MWh. This is because the prefix ‘Giga-‘ means one billion, and ‘Mega-‘ means one million, so there are 1,000 Megawatt-hours in a Gigawatt-hour.

GWh (Gigawatt-hours) measures energy, which is the total amount of power consumed or generated over time. MW (Megawatts) measures power, which is the rate at which energy is used or generated at a specific moment. For example, a 1 MW solar farm running for 1 hour produces 1 MWh of energy.

One GWh is equivalent to 1,000,000 kWh. In practical terms, 1 GWh can power approximately 33,000 UK homes for an entire day (assuming average daily consumption of 30 kWh per home), or it is roughly the amount of energy produced by a large gas-fired power plant running at full capacity for about an hour.

Large energy outputs, such as those from national grids, nuclear power stations, or total renewable energy generation, are measured in GWh (or TWh) because the numbers in kWh or MWh would be too large and cumbersome to read. Using GWh keeps the figures manageable and easier to compare.

The standard metric prefixes for watt-hours, from smallest to largest, are: Watt-hours (Wh), Kilowatt-hours (kWh, 1,000 Wh), Megawatt-hours (MWh, 1,000,000 Wh), Gigawatt-hours (GWh, 1,000,000,000 Wh), and Terawatt-hours (TWh, 1,000,000,000,000 Wh).

To convert MWh to GWh, you divide the number of Megawatt-hours by 1,000. For example, 5,000 MWh ÷ 1,000 = 5 GWh.