Flexi Says: Heat energy is measured as calories or kilocalories. A calorie is the amount of heat needed to raise the temperature of one milliliter of water one degree Celsius (°C). 1 kilocalorie (kcal) is 1000 calories. People seemed to find kilocalorie a big word, however, and started to use the word calorie instead. So the word calorie, abbreviated as Cal with a capital C, is used to mean kilocalorie especially in the context of food and nutrition.