A standard conversion in the International System of Units is that one calorie equals 4.186 joules, which is the amount of energy released as heat to raise 1 kg of water by 1 degree Celsius. As heat is a form of energy, it can be converted into joules. If there are 4.186 calories in a joule, then there are 0.2389 calories in a joule. To find calories per joule, divide calories by joules: 1/4.186 = 0.2389 cal/joule. Since 4,186 joules are equivalent to one calorie, it is the number of calories in one joule.