Kilojoules to Calories (kJ to kcal): converter and table

On food labels, Calories usually mean kilocalories. The uppercase C is common in consumer labeling. A kilocalorie is 1,000 small scientific calories. This guide uses kcal when it means the food-energy unit.

Kilojoules, written as kJ, are another unit for the same energy amount. A label can show kcal, kJ, or both. The numbers look different because the units have different sizes.

Convert the same energy amount in either direction

These rows apply the same factor to values that often appear on labels and in searches. Each result is rounded to one decimal place after the full calculation. Use the converter at the top of this page for any other number.

Kilojoules to kilocalories (divide by 4.184)

Kilocalories to kilojoules (multiply by 4.184)

Round after the conversion when you need a whole number. For example, 1,900 kcal equals 7,949.6 kJ before rounding. A label may show 7,950 kJ. The small display difference does not change the underlying amount.

Do not add kcal and kJ values together. Convert one value first, then compare values in the same unit. This also applies when a calculator uses kcal and a food label uses kJ.

1. Write kcal or kJ beside every energy number.
2. Convert before comparing two values from different labels.
3. Keep the unrounded value when you need to check the arithmetic.
4. Do not treat a unit conversion as a calorie target or a diet recommendation.

Use the macro calculator when you need to convert a stated kcal total and macro percentages into grams. Use the TDEE calculator when the question is about a daily energy estimate rather than a unit conversion.

A food-label Calorie is normally a kilocalorie, written kcal. A kilojoule, written kJ, is another unit of energy. For the thermochemical calorie convention used in this guide, 1 kcal equals 4.184 kJ. Multiply a kcal value by 4.184 to display the same energy in kJ; divide a kJ value by 4.184 to display it in kcal. The change in the number is a unit conversion. It does not add or remove energy from a food or establish how much someone should eat. Keep kcal and kJ visible so the figures are not mistaken for separate quantities.

The small scientific calorie and the food Calorie differ by a factor of 1,000. One kcal contains 1,000 small calories. This is why capitalization can matter in a textbook, yet food labels and apps often use the word calorie informally for kcal. The United States Nutrition Facts label calls its food-energy number Calories. Before converting a number from an unfamiliar source, check whether its definition is kcal, cal, or kJ. Treating a small-calorie figure as a food-label Calorie creates a thousand-fold mistake, far larger than any rounding difference in a normal label.

For a hypothetical amount of 500 kcal, multiply 500 × 4.184 to get 2,092 kJ. To check the conversion, divide 2,092 kJ by 4.184 and recover 500 kcal. The reverse operation is useful because it catches a common error: multiplying when the starting value is already in kJ. The unit tells you which operation to use. A larger kJ number does not mean more food energy than its corresponding smaller kcal number; both numbers describe the same amount on different scales.

The National Institute of Standards and Technology lists the thermochemical calorie as 4.184 joules and the thermochemical kilocalorie as 4,184 joules. Since 1 kJ is 1,000 joules, that kilocalorie is 4.184 kJ. NIST also lists other historical calorie definitions with slightly different conversion factors. This guide uses the thermochemical convention consistently. If a scientific source names another calorie definition, use its stated factor for that source instead of silently changing it to 4.184. Food-energy calculations usually do not need that level of distinction, but the unit label should remain clear.

A label value often applies to one serving, not to an entire package. Suppose a hypothetical label shows 500 kcal per serving and the package contains two servings. One serving is 2,092 kJ after conversion. The whole package, under the label's stated serving count, is 1,000 kcal or 4,184 kJ. Multiplying by the serving count and converting units are separate operations. You can do them in either order when you retain the full values: 500 × 2 × 4.184 gives the same result as 500 × 4.184 × 2. Write both the energy unit and the serving basis in the final record.

If another label shows 1,200 kJ per serving, divide by 4.184 to get about 286.8 kcal per serving before display rounding. To compare that serving with the 500 kcal serving, put both on a per-serving basis and in one energy unit. A package-to-serving comparison can be misleading even when every conversion is mathematically correct. Likewise, a daily calculator estimate in kcal/day is not directly comparable to a single food label's kcal/serving until you decide what period and amount you mean. The unit and the denominator both matter.

An illustrative 1,900 kcal equals 7,949.6 kJ. A display that uses whole kilojoules may show 7,950 kJ. If you convert 7,950 kJ back, you get a value close to 1,900 kcal, with a small difference from rounding. Keep the unrounded value while you do intermediate arithmetic. When you add many rounded label numbers, the total may differ slightly from a total calculated from unrounded values. The difference can reflect display precision rather than a changed energy amount.

Rounding the factor itself too early has a larger effect. Using 4.2 in place of 4.184 changes a 1,900 kcal conversion to 7,980 kJ, 30.4 kJ above the unrounded result. That may be acceptable for a rough mental estimate if you mark it as such, but it is not the exact conversion used by this guide. The shortcut 1 kcal is about 4.2 kJ can help you check whether an answer has the right scale. Use 4.184 when reproducing a calculator value or comparing records that need consistent arithmetic.

Adding 500 kcal and 1,200 kJ as if both numbers were kcal gives a meaningless 1,700-unit total. Convert first: 1,200 kJ is about 286.8 kcal, so the two hypothetical amounts total about 786.8 kcal. Expressed in kilojoules, the same total is 2,092 + 1,200 = 3,292 kJ. Multiplying 786.8 rounded kcal by 4.184 will come close to 3,292 kJ; using the unrounded 1,200 ÷ 4.184 value gives the exact equality. This example shows why unit conversion belongs before addition or subtraction.

A calorie target, energy-expenditure estimate, and food label may also use different time bases. A daily estimate is written kcal/day or kJ/day; a food label usually gives energy per serving. Unit conversion alone cannot turn a serving into a daily total. You need the number of servings or a full daily record for that comparison. Body Numeral’s TDEE calculator estimates daily energy under its own assumptions. The kcal-to-kJ factor can restate that result in another unit, but it cannot improve the estimate or make it a measured personal expenditure.

Calories on a label are an energy declaration for the stated amount of food. The Food and Drug Administration explains that the Nutrition Facts Calorie number describes energy per serving. Two foods can show the same Calories while differing in nutrients and serving size. A kcal-to-kJ conversion preserves the energy number; it says nothing about protein, fibre, food quality, or suitability for a person. If you use the macro calculator, its kcal-per-gram factors perform a different conversion from energy shares to estimated nutrient grams. Do not apply the 4.184 factor in place of those macro factors.

A useful audit trail is short: copy the source number, its energy unit, its serving or time basis, the conversion operation, and the displayed rounding. If a label already shows both kcal and kJ, compare them with the 4.184 factor, allowing for the label's rounding. Do not add the two displayed columns together; they represent the same declared energy. If the columns appear far apart after conversion, check the serving basis and the unit before assuming the label or calculator is wrong.