The kilojoule (kJ) equals 1,000 joules and is the standard unit for expressing food energy content and chemical reaction energies in countries using the metric system. Food labels in Australia, Europe, and many other regions display energy values in kilojoules alongside or instead of calories. One kilojoule equals approximately 238.8 calories or about 0.239 kilocalories.

The calorie (cal) is a small energy unit defined as the amount of heat needed to raise one gram of water by one degree Celsius, primarily used in physics and chemistry. In everyday language, 'calorie' usually refers to the kilocalorie (kcal), but the true calorie is 1/1,000th of that amount. One calorie equals exactly 4.184 joules, providing a direct bridge between thermal and mechanical energy.