In my attempt to count calorie in food, I was confused by the units - calories and kilocalories. I came across food labels that told me that a small 30g serving of cereal gave me 300kcal, and this kept me wondering if this was the same as 300cal since we all knew that an average adult required about 2000 calories of intake. And if "kilo" equates to the amount of "1000" units and 300kcal actually meant 300 000 calories, then 30g of cereal would be sufficient to sustain many days of activities! How logical is that? Surely, there is more than it meets the eye...
A quick research helped to demystify "kcal" and "calories". I learned this:
Scientifically, 1 kilocalorie=1000 calories=1 kcal= the energy it takes to raise the temperature of 1kg of water by 1°C.
Calories are units of energy so small that a tiny cookie can provide thousands of them. To ease calculations, energy is expressed in 1000-calorie units known as kilocalories. That is, 1 Calorie is equivalent to 1 kilocalorie; the capital C in Calories denotes kcal. However, in dietary nutrition context, while values are given for the number in kilocalories in a food, they are usually simply referred to as calories. As a result, this creates much confusion over the difference between "kcalorie" and "calories".
On food labels, calories and kilocalories are used interchangeably to mean the same thing. In other words, it is just as normal and acceptable for people to use the small "c" instead of big "C" and say "1 gram of fat gives us 9 calories" in the nutrition world as "1 gram of fat gives us 9 kilocalories or 9000 calories" in the physical science world. (In some instances, you might have also seen food packaging displaying kJ values, which is kilojoule. 1 kilojoule = 4.2 kilocalories.)