Check the label of the food you're investigating. If the label is not present, check the nutrition information to determine the amount in grams of proteins present in the product. Multiply the grams of proteins by four to obtain the kilocalories of the protein section of the product.
Check on the nutrition list again to see the fat grams present in the food. To find the number of kilocalories of the fats section, multiply the grams of fat by nine to observe the energy in kilocalories.
Observe again the nutrition list to find the grams of carbohydrates present. To calculate the kilocalories, multiply the grams of carbohydrates by four to get the number of kilocalories of the carbohydrate section.
Add up the individual calories using the calculator to obtain the total number of kilocalories in the food product.
Multiply the figure you had earlier obtained by 1,000 to convert the kilocalories into calories. This is because the prefix "kilo-" denotes 1,000. If, for example, the figure you had obtained was 2.5 kilocalories, the figure now in units of calories will become 2,500 calories
Divide the total number of calories by the conversion constant 0.239. This will result in 10,460.25 joules rounded off to two decimal points.
Divide the figure in joules by 1,000 to convert the energy amount in joules into kilojoules as the obtained figure is large. In this case, the division results in 10.460 kilojoules approximated to two decimal points.