Convert Calorie to Kilojoule (cal → kJ)

The calorie is the chemistry energy unit, equal to 4.184 joules and used in thermochemistry calculations.

Calorie

Kilojoule

0.004184

1 cal0.004184 kJNIST · BIPM accuracy

Calorie to Kilojoule Conversion Table

10 common values

Calorie	Kilojoule
1 cal	0.004184 kJ
10 cal	0.04184 kJ
100 cal	0.4184 kJ
500 cal	2.092 kJ
1,000 cal	4.184 kJ
5,000 cal	20.92 kJ
10,000 cal	41.84 kJ
50,000 cal	209.2 kJ
100,000 cal	418.4 kJ
500,000 cal	2,092 kJ

How to Convert Calorie to Kilojoule Manually

Step by Step

Converting calories to kilojoules is straightforward: multiply by the conversion factor. Follow these three steps to do it by hand or in your head.

1
Take your value in calories
Start with the number of calories (cal) you want to convert.
2
Multiply by 0.004184
The conversion factor from cal to kJ is 0.004184. Multiply your value by this number.
3
Read the result in kilojoules
The result is your value in kilojoules (kJ).

Practical Examples

1 cal

equals

0.004184 kJ

5 cal

equals

0.02092 kJ

10 cal

equals

0.04184 kJ

25 cal

equals

0.1046 kJ

100 cal

equals

0.4184 kJ

Formula

Multiply the value in calories by 0.004184. For the reverse direction, multiply by 239.00574.

ForwardkJ = cal × 0.004184

Reversecal = kJ × 239.00574

Example: 10 cal × 0.004184 = 0.04184 kJ

Tips

Use these in everyday conversions

1 cal = 4.184 J. 1 kcal = 4184 J.
Scientific "calorie" and nutrition "Calorie" differ by 1000×.
Prefer joules in modern scientific writing.

Common Mistakes

Avoid these

Assuming "calories" on food labels means gram calories — they are kcal.
Mixing gram calories and kilocalories in calculations.
Confusing calorie (energy) with calorimeter (apparatus).

About Calorie and Kilojoule

What is the Calorie?

The calorie equals exactly 4.184 joules (the 'thermochemical calorie') and is the historical unit for heat in chemistry and physics. It was originally defined as the heat needed to raise 1 gram of water by 1°C (a definition that varied slightly with starting temperature, hence multiple 'calories' — 4.184 J was set as the exact thermochemical convention). The calorie is widely used in older physics and chemistry literature for reaction energies, specific heat capacities, and thermodynamic calculations. Note: this 'small calorie' (lowercase c) is 1/1000 of the food Calorie (capital C) used in nutrition. The chemistry calorie relates to the joule (4.184 J = 1 cal), the kilocalorie (1,000 cal = 1 kcal = 1 food Calorie), and the BTU (1 BTU ≈ 252 cal). Modern SI usage in scientific publications has largely replaced the calorie with the joule, but it persists in medical and chemistry contexts.

Thermodynamics and older physics texts
Chemistry energy calculations
Some engineering heat-transfer contexts

Real-world examples

Raising 1 g of water 1 °C: 1 cal. A 100 kcal snack = 100,000 small calories.

What is the Kilojoule?

The kilojoule equals 1,000 joules and is the standard unit on European nutrition labels and in mid-scale chemical and physical calculations. EU regulations require food packaging to display energy in kilojoules (typically with kilocalories also shown for consumer familiarity): a chocolate bar might show '2,100 kJ / 500 kcal' per 100 g. The kilojoule is also common in chemistry (bond energies), electrical engineering (capacitor storage), and small-mechanical-energy contexts. A car battery typically stores about 1,800 kJ; lifting a person 1 meter requires roughly 0.7 kJ. The kilojoule relates to the joule (1,000 J = 1 kJ), the kilocalorie (1 kcal = 4.184 kJ), the watt-hour (1 kWh = 3,600 kJ), and the megajoule (1,000 kJ = 1 MJ). The conversion factor 4.184 (kJ per kcal) is one of the most-used numbers in nutrition labeling.