Energy Converter

Convert an amount of energy into kcal, kJ, J, Wh, kWh, MJ and cal at once.

Energy to convert

Unit of the energy

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Result (— equals) —

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Copy with high precision (15 digits)

Values are shown with 7 significant digits (rounded). Very small values (below 0.000001) and very large values (10¹⁵ or more) use scientific notation such as 6.213712e-7. The values copied are shown below the buttons, without commas. When a value is rounded, it is labeled "rounded value".

Energy units and their definitions

The size of each unit in joules is listed below. The converter first turns your value into joules, then divides by the size of each unit.

The calculation uses exact fractions, and the only rounding is the one applied when a value is displayed.

Which calorie does this tool use?

The word "calorie" has more than one definition. NIST SP 811 lists three, all in joules:

• Thermochemical calorie (cal_th): exactly 4.184 J. This is the value this tool uses for 1 cal. A kilocalorie (kcal) is 1,000 cal, which is 4,184 J (4.184 kJ).
• International Table calorie (cal_IT): exactly 4.1868 J. About 0.07% larger. It is not used here.
• Mean calorie: about 4.19002 J. It is not used here.

The kilogram calorie, or "large calorie", is an obsolete name for the kilocalorie, which is the calorie used to express the energy content of foods (NIST SP 811, footnote 11). Food labels in some countries use kcal and others use kJ. Which calorie definition a particular label uses is not something this tool can tell you, so if you need to match a label exactly, check the definition that applies.

If you work with the International Table calorie, the results here are about 0.07% too small compared with that definition (1 kcal_IT is 4.1868 kJ, against 4.184 kJ here).

Examples

• 1 kcal = 4.184 kJ, and 100 kcal = 418.4 kJ
• 1 kJ = about 0.2390057 kcal
• 1 Wh = 3.6 kJ = 3,600 J
• 1 kWh = 3,600 kJ = about 860.4207 kcal (using 4.184)
• 2,000 kcal = 8,368 kJ

Notes

• You can enter decimals (up to 12 digits before the decimal point and 6 decimal places). Use a period as the decimal separator. Commas are accepted only as thousands separators, for example 1,234.5.
• This tool only converts units. It does not calculate nutrition, the calories in a meal, or how much energy a person needs.
• Energy and power are different quantities. A watt-hour (Wh) is an amount of energy, while a watt (W) is a rate. For power units, see the Power Converter.

Sources

The definitions on this page come from the sources below (checked on November 1, 2026). The calorie, kilowatt-hour and watt-hour rows of NIST SP 811 Appendix B.8 and B.9 were read word for word. Appendix B marks exact factors in boldface. The text of footnotes 10 and 11 was read on the NIST footnotes page: NIST Guide to the SI, footnotes.

• NIST Special Publication 811, Appendix B.8: Factors for units listed alphabetically
• NIST Guide to the SI, Appendix B.9: Factors for units listed by kind of quantity or field of science (pressure or stress)

Frequently asked questions

How many kJ is one kcal?

4.184 kJ (using the thermochemical calorie, 1 cal = 4.184 J). 100 kcal is 418.4 kJ.

How do I convert kJ to kcal?

Divide by 4.184. For example, 1,000 kJ is about 239.0057 kcal.

How many kcal are in one kWh?

About 860.4207 kcal (3,600 kJ ÷ 4.184). One kWh is the energy used by a 1 kW load running for one hour, which is 3,600 kJ.

What is the difference between cal and kcal?

1 kcal is 1,000 cal. Food energy is usually given in kcal (sometimes written "Calories" with a capital C) or in kJ.