Gigajoules to megawatt hours converter above calculates how many megawatt hours are in 'X' gigajoules (where 'X' is the number of gigajoules to convert to megawatt hours). In order to convert a value from gigajoules to megawatt hours (from GJ to MWh) type the number of GJ to be converted to MWh and then click on the 'convert' button.