Gigajoules to kilocalories conversion calculator shown above calculates how many kilocalories are in 'X' gigajoules (where 'X' is the number of gigajoules to convert to kilocalories). In order to convert a value from gigajoules to kilocalories (from GJ to kcal) type the number of GJ to be converted to kcal and then click on the 'convert' button.