Millijoules to Kilocalories (mJ to kcal)

1 millijoule equals 2.390057361×10⁻⁷ kilocalories (rounded).

1 millijoule = 2.390057361×10⁻⁷ kilocalories

How to convert millijoules to kilocalories

To convert millijoules to kilocalories, multiply the number of millijoules by 2.390057361×10⁻⁷. The factor is rounded to 10 significant digits. To go the other way, multiply kilocalories by 4,184,000.

kilocalories = millijoules × 2.390057361×10⁻⁷

Example: 10 millijoules = 0.000002390057361 kilocalories.

The 'calorie' on food labels is really a kilocalorie. The thermochemical calorie (4.184 J) is used here unless marked IT.

About these units

Millijoule (mJ)

Metric (SI)Current unit

One thousandth of a joule. Used for very small amounts of energy.

Prefixing the joule with milli gives a unit one thousandth of the base size, so 1 mJ is 0.001 J. The joule itself honours the English physicist James Prescott Joule, and its name was proposed by Wilhelm Siemens in 1882 before adoption at the 1889 International Electrical Congress. Because the joule equals one watt-second, a millijoule is also a milliwatt applied for one second, which makes it a natural size for tiny electrical budgets.

Some verifiable comparisons show the scale. One list of energy magnitudes puts an atomic battery's output over an hour at about 3 mJ, and an LED running for a second at about 40 mJ. A half-dollar coin dropped from a metre releases roughly 110 mJ. In atomic units, one millijoule is about 6.24 x 10^15 electronvolts, using the exact electronvolt value of 1.602176634 x 10^-19 J. Below the millijoule come the microjoule and nanojoule, so it sits at the coarse end of small-energy measurement.

1 millijoule = 0.001 joules (exactly).

Sources: Wikipedia: Joule; Wikipedia: Orders of magnitude (energy); Wikipedia: Electronvolt

Kilocalorie (kcal)

ScientificTraditional unit (still used in some regions)

1,000 thermochemical calories (4,184 J). The 'Calorie' on food labels in North America.

Marcellin Berthelot separated the gram calorie from the kilogram calorie in 1879, and the American chemist Wilbur Atwater adopted a capital-C Calorie for the large unit in 1887 in a widely read article on the energy in food. Joseph Howard Raymond proposed the term kilocalorie in his 1894 textbook. The two names now describe the same quantity, 1,000 small calories, which at the thermochemical value is 4,184 J or 4.184 kJ.

Food labels carry the unit today, though practice differs by region. North American labels use kilocalories almost exclusively, European labels show kilojoules and kilocalories together under EU Regulation 1169/2011, and Chinese labels give kilojoules only. Typical energy contents are about 9 kcal per gram for fat, about 4 for carbohydrate and protein, and about 7 for alcohol. In electrical terms, 4,184 J works out to about 1.162 watt-hours, since one watt-hour is 3,600 J. NIST also lists a kilocalorie based on the International Table calorie, which is 4,186.8 J.

1 kilocalorie = 4,184 joules (exactly).

Sources: Wikipedia: Calorie (includes kilocalorie); NIST SP 811, Appendix B.8 (energy conversion factors)

Related conversions

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