Difference Between Calories and Kilojoules

Calories vs Kilojoules

Calories and kilojoules are units to measure the energy. Commonly, these two words are used in measuring food energy. It is necessary to indicate the amount of energy contained in each food item on their packagings. Some countries indicate the energies of food in calories, and some countries indicate it in kilojoules.


A calorie is defined as “the amount of heat energy required to raise the temperature of 1 gram of water up by 1 oC.” Calorie is mainly used to measure the food energy. 1 kilocalorie is equaled to 1000 calories. In food packaging, the energy value is mostly given in kilocalories or the word “Calorie”, which has the same meaning as kilocalorie. Therefore, “calorie” and “Calorie” have two different meanings in food chemistry.

Obesity is a common problem these days; therefore, people are much concerned about the calories they take into their bodies. Not only for this, it is important to know the energy amount of food we are taking, in order to maintain a healthy body. Foods are needed in our body to produce energy. For example, 1 g of carbohydrate and 1 g of protein normally contain 4 Calories and 1 g of fat contains 9 Calories. The food we are taking in, undergo a process called metabolism. In this process, the chemical energy stored in food is converted into the chemical energy of ATP. ATP is needed to provide energy to all the functions in the body. If there is an excess amount of calorie consumption than the calories burned in the body, they will be stored as fat. As a result of that the body weight will increase. To control the weight gain, people can increase the burning rate of stored fat by exercising. However, if the consuming energy is less than what we want, then the body weight reduces. Different people need different calorie intakes per day depending on the age, gender, size, environment and their daily activities. For example, children, athletes, and hard working people need more energy than elderly people.


Kilojoules is the SI unit to measure energy. 1000 joules are equivalent to a 1 kilojoule. Joule has different definitions based on what energy it is used to measure. It can be defined as the energy needed to apply a 1 force of Newton to move 1 m distance. In terms of electric energy, it is “the work required to move an electric charge of one coulomb through an electrical potential difference of one volt. “ In terms of food chemistry, 1 kilocalorie/Calorie is equal to 4.184 kilojoules.


It is important to know the energy conversions, because Calorie and kilojoules are interchangeably used in food packaging. By knowing this you can be aware of how much energy you are taking into the body from each food.

4.184 kilojoules = 4,184 joules = 1 Calorie = 1 kilocalorie = 1,000 calories

Difference Between Calories and Kilojoules

- Calorie/kilocalorie is a larger unit to measure energy compared to kilojoule.

- The unit Calorie is often used to indicate food energy, but the unit kilojoule uses for a wider variety of energy indications.