Energy Converter
Convert between joules, kilocalories, kilowatt-hours, BTU, electronvolts, and other energy units.
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How to use this calculator
- 1
Enter the energy value you want to convert.
- 2
Select the unit you are converting from (e.g. kilocalories).
- 3
Select the target unit (e.g. kilojoules).
- 4
The result updates instantly.
Frequently asked questions
How many kJ are in a kcal?
One kilocalorie is 4.184 kJ, or 4,184 J, using the thermochemical calorie. So a 2,000 kcal diet is 8,368 kJ. Food labels that say Calories with a capital C mean kilocalories, which is why 100 kcal is 418.4 kJ.
Is a calorie the same as a kilocalorie?
No. A small calorie (cal) is 4.184 J and a kilocalorie (kcal) is 1,000 of them, 4,184 J. The food Calorie is the kilocalorie. The International Table calorie of 4.1868 J, about 0.07 percent larger, is not what this tool uses.
How many kWh equal one joule, and vice versa?
One kilowatt-hour is exactly 3,600,000 J, or 3.6 MJ, and one watt-hour is 3,600 J. So 1 J is 2.7777778e-7 kWh. A kWh is also 860.4206501 kcal and 3,412.141633 BTU.
Which BTU does the converter use?
It uses 1,055.05585262 J, the International Table BTU. Other definitions of the BTU, such as the thermochemical one, differ by roughly 0.07 percent, which is small but can show up if you compare with older tables.
Why is BTU/h not here?
BTU is energy, while BTU/h is power. This converter does not handle rates. Converting 12,000 BTU gives 3.516852842 kWh, but a 12,000 BTU/h air conditioner is about its power, and for that use the power converter.
What is an electronvolt in joules?
Exactly 1.602176634e-19 J, the value fixed in the 2019 SI. A joule is therefore about 6.241509e+18 eV. The unit is used for particle and atomic energies, so values appear in scientific notation.
What is the foot-pound unit here?
A foot-pound-force of energy, 1.3558179483 J, the work of one pound-force through one foot. Its number matches the torque unit lbf·ft in N·m, but energy and torque are different quantities, so use the torque converter for twisting force.
Energy units: joules, calories, kilowatt-hours and BTU
Calories come in sizes
The calorie used here is the thermochemical calorie, exactly 4.184 J. A kilocalorie is 4,184 J, and the Calorie on food packaging is a kilocalorie. A watt-hour is 3,600 J, so a kilowatt-hour is 3.6 million joules. The BTU is 1,055.05585262 J, and the electronvolt is exactly 1.602176634e-19 J. Every conversion in the tool passes through joules. These definitions let you move across very different fields: a diet in kcal, an electricity bill in kWh, a heating spec in BTU and an atomic energy in eV all reduce to joules.
Reference values taken from the converter
Each row begins with one energy unit and shows the same energy in joules, kilocalories, kilowatt-hours and BTU, copied from the tool’s output.
| From | Joules | kcal | kWh | BTU |
|---|---|---|---|---|
| 1 kWh | 3,600,000 | 860.4206501 | 1 | 3,412.141633 |
| 1 kcal | 4,184 | 1 | 0.0011622222 | 3.965666831 |
| 1 BTU | 1,055.055853 | 0.2521644 | 0.00029307107 | 1 |
| 1 Wh | 3,600 | 0.86042065 | 0.001 | 3.412141633 |
| 1 kJ | 1,000 | 0.23900574 | 0.00027777778 | 0.94781712 |
Worked examples: diet and electricity
A 2,000 kcal day equals 8,368 kJ, or 2.324444444 kWh. A 500 kJ serving is 119.5028681 kcal and 138.8888889 Wh. In the other direction, 10 kWh of electricity is 36,000 kJ or 34,121.41633 BTU. For heating, 12,000 BTU of heat is 3.516852842 kWh, or 12,660.670231 kJ. A single 100 kcal snack therefore holds 418.4 kJ, or 116.2222222 Wh. Pushing a pound-force through one foot does 1.355817948 J of work, which is 0.0012850675 BTU.
Energy is not power
Energy is an amount (joules, kWh, BTU), and power is the rate at which it is used (watts, BTU per hour). A 3 kW heater running for two hours uses 6 kWh. The converter cannot add time, so a rating of BTU/h or kW needs the power converter. This is the reason 12,000 BTU and 12,000 BTU/h are not interchangeable.
Where the converter stops
The tool does not model efficiency, fuel energy content or tariffs. It handles nine units only, and electronvolt results appear in scientific notation because they are so small. Rounding to ten significant digits is cosmetic. Heat content of fuels, battery capacity in Wh or mAh and tariff rates are all outside this tool, though Wh and kWh are in the list and so are directly usable for batteries.
Learn more from an authoritative source:
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Results are estimates for informational purposes only and do not constitute professional financial, medical, legal, or technical advice. Read full disclaimer →