Megajoules to megawatt hours conversion calculator shown above calculates how many megawatt hours are in 'X' megajoules (where 'X' is the number of megajoules to convert to megawatt hours). In order to convert a value from megajoules to megawatt hours (from MJ to MWh) just type the number of MJ to be converted to MWh and then click on the 'convert' button.