WTF is a calorie?

A calorie is a measure of energy content in a food. It is the amount of energy required to raise the temperature of 1 gram of water by 1 degree Celsius, assuming you could convert 100% of it to heat energy. When you see “calorie” written out in nutrition handbooks and labels, which is sometimes capitalized, it is referring to kilocalories, or 1000 calories. That is the the energy required to raise the temperature of 1 kilogram of water by 1 degree Celsius. However, many countries use kilojoules, abbreviated “kJ”, on their labels. A kilojoule is equivalent to 1000 joules or 0.239 kilocalories. A joule is the amount of energy required to displace a mass by 1 meter using 1 newton of force. How much of that do you need to know? None of it, except that when you see kilojoules on the label, simply divide by 4 to get a rough estimate of the calories. Now you know.