We imagine that you have heard the word ‘calorie’ before, but before we can go much further it’s probably a good idea to define the term. Calories are measurements of energy, in much the same way as millilitres are a measurement of liquid or centimetres are a measurement of distance. As such, a calorie has a specifically determined and universally agreed value which is 4.184 joules. A calorie is a very small unit, though, so the unit used to determine energy for our purposes here are kilo calories, often represented as kcal or Calories with a capital C, which is equivalent to 1000 calories or 4180 joules.
This unit is the amount of energy required to raise the temperature of 1kg of water by 1 degree Celsius.
It’s important to remember that calories have a well-defined and universally agreed value because, ultimately, a calorie is the same regardless of its source. It’s a lot more complex than that in practice, as you’ll see, but this is worth remembering from the outset.