Strictly, a calorie is the amount of heat required to raise the temperature of 1 gram of water by 1 °C. This is a very small amount, and dietitians found it more convenient to use the kilocalorie (kcal), 1,000 calories, in their calculations. Unfortunately they called this a ‘Calorie’ with a capital C. The use of the capital was often misunderstood or omitted, causing much confusion. In popular usage 1 kcal is ‘a calorie’.