A calorie was originally defined as the amount of energy required to raise the temperature of one gram of water by one degree Celsius. One calorie = 4.184 J. One kcal = 1,000 cal. When we count calories in our food, we are actually referring to kilocalories; e.g. 1 dietary Calorie = 1,000 cal = 1 kcal. See: The note in the previous entry for information about the mole part of this unit