In this article (8 sections)
What Do Calories Measure?
Calories describe the energy in food and drink. The body uses energy both at rest and during activity. The calorie count alone does not indicate which nutrients a meal contains. The NHS explanation of calories also distinguishes between the energy in food and the body's energy expenditure.
What is the Difference Between kcal and kJ?
Both measure energy. Use kcal × 4.184 = kJ and kJ ÷ 4.184 = kcal. You can try the calculation in the kJ/kcal converter, where the conversion basis is also provided.
How do US Nutrition Facts labels work?
US labels usually give calories for the stated serving; some containers also show package information. The FDA calorie-label guide explains why 2,000 calories is a reference rather than your personal daily need.
For a hypothetical cereal labeled 160 kcal per 40 g serving, eating 60 g gives 160 x 60 / 40 = 240 kcal. Check the servings per container. A labeled serving describes the food amount used for the nutrition information; it is not automatically the portion you should eat.
Imported European products may use per-100-g values and show kJ as well as kcal. Identify the unit basis before comparing them with a US serving-based label.
Where Do Calories in Food Come From?
The energy in food comes from fat, carbohydrate, protein, and alcohol, with a small amount from dietary fiber. The table below describes European labeling factors, useful for understanding imported food tables rather than applying one fixed rule to every US nutrient calculation. Nutritional declarations in the EU use fixed factors per gram, as stated in Annex XIV to Regulation (EU) No 1169/2011 on food information:
| Nutrient | kJ per gram | kcal per gram |
|---|---|---|
| Fat | 37 | 9 |
| Alcohol | 29 | 7 |
| Protein | 17 | 4 |
| Carbohydrate | 17 | 4 |
| Polyols (e.g., sorbitol) | 10 | 2.4 |
| Dietary fiber | 8 | 2 |
In this labeling calculation, fat provides more than twice as much energy per gram as protein and carbohydrate. Foods rich in fat are therefore often energy-dense.
For a simplified calculation, 100 grams of fat gives 100 × 9 = 900 kcal. Real food labels and databases may use different energy conventions and rounding, so use the stated energy for the product or database record. The original Danish article used FRIDA 6.1 examples; these historical figures are not USDA measurements. Current Calorie.one lookups use USDA FoodData Central and Open Food Facts.
Why Do Packages Show Both kJ and kcal?
EU nutrition declarations generally express energy in both kJ and kcal, with values per 100 grams or 100 milliliters. Portion information can appear alongside them. Some foods and forms of presentation have exemptions or special rules; use the actual label and its stated basis when comparing products.
From Food Label to Portion
A hypothetical product with 200 kcal per 100 grams provides 150 kcal in a portion of 75 grams: 200 × 75 ÷ 100 = 150. Weigh the amount you eat and check whether the declaration applies to raw or cooked food.
If the declaration uses milliliters, the portion must also be in milliliters. Grams and milliliters can only be exchanged when the product's density is known.
Calories in Food or Your Daily Requirement?
The calorie calculator helps with a meal. The daily calorie needs calculator provides an estimate of an adult's daily energy expenditure. These are two different calculations, and neither is a measurement of your body.
See also protein, carbohydrate, and fat if you want to understand the figures alongside the calories.
Frequently Asked Questions
Is a Calorie and a kcal the Same?
In everyday language, yes. When "calories" are mentioned in relation to food, it means kilocalories, kcal. Strictly speaking, a kilocalorie is 1,000 calories, but in calorie tables, apps, and on this page, the word calorie is used to mean kcal.
How Many kJ are 100 kcal?
100 kcal is 418.4 kJ, because 1 kcal is 4.184 kJ. Conversely, 1,000 kJ is approximately 239 kcal. The kJ/kcal converter calculates it for you.
Is 100 kcal from Fat the Same as 100 kcal from Sugar?
The amount of energy is the same. The difference is what else the food contains in terms of protein, dietary fiber, vitamins, and minerals, and this is not reflected in the calorie count. See protein, carbohydrate, and fat.
Where Do the Calorie Figures on Calorie.one Come From?
Current food lookups use USDA FoodData Central and Open Food Facts. Historical article examples that use FRIDA 6.1 remain labeled with their original source. How database matches and estimates are distinguished is explained on the method page.