It is said that calorie is not always a calorie. Because there are two types of calorie and both differ in magnitude. The ‘small’ or fundamental calorie is the amount of heat required to raise the temperature of 1 gram of water by 1⁰ Celsius and is equal to 4.185 joules. This is the gram-calorie used in physics and chemistry.
The ‘large’ of international calorie you see in diet books and on food labels is the amount of heat energy required to raise the temperature of 1,000 grams (one kilogram) of water by 1⁰ Celsius. It is appropriately called the kilocalorie, though the term is seldom used by nutritionists. A kilocalorie is equal to 4.19 kilojoules or kJ. To avoid any possible confusion, the nutritionist’s or ‘large’ calorie is written with capital ‘C’.