Unit of measurement for energy. One calorie is formally defined as the amount of energy required to raise one cubic centimeter of water by one degree Centigrade. For purpose of measuring the amount of energy in food, nutritionists most commonly use kilocalories (equal to 1000 calories), and label the measurement either as “kcal” or as “Calories” with a capital “C”. One kcal is also equivalent to approximately 4.184 kilojoules.