Kilocalories to kilojoules (kcal to kJ) converter

What is a kilocalories to kilojoules converter?

A kilocalories to kilojoules converter is an online tool that translates an amount of energy expressed in kilocalories (kcal) into its equivalent value in kilojoules (kJ), and vice versa. Both units measure the same physical quantity—energy—but they belong to different traditions. The calorie comes from the older, heat-based system of units, while the joule is the official energy unit of the International System of Units (SI). Because food labels, nutrition guides, and scientific papers often mix the two, a quick way to move between them is genuinely useful.

The converter also handles related units such as joules (J) and megajoules (MJ), so you can scale your figure up or down without leaving the page.

Where you will see kcal and kJ

You encounter both units more often than you might think:

• Nutrition and diet: Food energy is labelled in kilocalories (often just called “Calories”) in some countries and in kilojoules in others, such as Australia and across much of the EU where both appear side by side.
• Fitness tracking: Wearables and gym equipment may report energy burned in either unit depending on the region or brand.
• Chemistry and physics: Reaction enthalpies and physical work are usually reported in joules or kilojoules, so converting from older calorie-based data is common.
• Engineering and heating: Thermal energy is frequently quoted in kilojoules, while legacy data may still appear in kilocalories.

How does the converter work?

The relationship between the two units is fixed and defined by the thermochemical calorie: one kilocalorie equals exactly 4.184 kilojoules. To convert kilocalories to kilojoules you multiply by 4.184; to convert back you divide by the same factor (or multiply by its reciprocal, about 0.239006). Enter a number in either field and the other field updates instantly, so you can read the conversion in whichever direction you need.

Formula for conversion

The core conversions rely on the constant 4.184:

For kilocalories to kilojoules: $\text{kJ} = \text{kcal} \times 4.184$

For kilojoules to kilocalories: $\text{kcal} = \text{kJ} \times 0.239006$

If you need joules instead of kilojoules, simply multiply the kilojoule result by 1000: $\text{J} = \text{kcal} \times 4184$

Kilocalories to kilojoules conversion table

The table below lists common kilocalorie amounts and their kilojoule equivalents, using the factor 4.184:

Examples

Example 1: A single kilocalorie

Convert 1 kilocalorie to kilojoules. Multiply by the fixed factor:

$1 \text{ kcal} \times 4.184 = 4.184 \text{ kJ}$

So 1 kcal equals exactly 4.184 kJ.

Example 2: Reading a food label

A snack lists its energy as 100 kcal. To express that in kilojoules, multiply by 4.184:

$100 \text{ kcal} \times 4.184 = 418.4 \text{ kJ}$

The same snack therefore carries 418.4 kJ of energy.

Example 3: Converting back to kilocalories

Suppose a label shows 4.184 kJ and you want kilocalories. Divide by 4.184 (or multiply by 0.239006):

$4.184 \text{ kJ} \times 0.239006 = 1 \text{ kcal}$

The value returns cleanly to 1 kcal, confirming the reverse direction.

Example 4: Switching to joules

If you prefer joules over kilojoules, 1 kilocalorie becomes:

$1 \text{ kcal} \times 4184 = 4184 \text{ J}$

That is the same energy as 4.184 kJ, just expressed in the smaller base unit.

Notes

• The factor 4.184 comes from the thermochemical calorie, the definition most widely used in nutrition and chemistry. A slightly different value (about 4.1868) applies to the International Steam Table calorie, but the difference is negligible for everyday use.
• A nutritional “Calorie” with a capital C is the same as one kilocalorie, which is why a 2000 Calorie diet is really 2000 kcal.
• Keep your units consistent throughout a calculation to avoid mixing kilojoules with joules by a factor of 1000.

Frequently asked questions

How many kilojoules are in 1 kilocalorie?

One kilocalorie equals exactly 4.184 kilojoules. This is a defined constant, so the conversion is always precise.

How do I convert kilocalories to kilojoules manually?

Multiply the number of kilocalories by 4.184. For example, 100 kcal × 4.184 = 418.4 kJ.

How do I convert kilojoules back to kilocalories?

Divide the kilojoule value by 4.184, or multiply it by 0.239006. For instance, 4.184 kJ ÷ 4.184 = 1 kcal.

Is a Calorie the same as a kilocalorie?

Yes. The “Calorie” shown on food packaging (with a capital C) is identical to one kilocalorie, equal to 1000 small calories. If you need to work with small calories, you can use our calorie to kilojoule converter.

Why do food labels sometimes show both kJ and kcal?

Many regions require energy to be stated in kilojoules as the SI unit, while kilocalories remain familiar to consumers. Showing both lets everyone read the value in their preferred unit.

How many joules are in 1 kilocalorie?

Since 1 kJ equals 1000 J, one kilocalorie equals 4.184 × 1000 = 4184 joules.