Energy Converter
Convert joules, calories, kWh, BTU, and electronvolts.
Enter a value, choose the units, and see the result plus every other energy unit.
Kilocalorie (food Calorie) → Kilojoule
Energy Converter
Convert energy between joules, kilojoules, megajoules, calories, kilocalories, watt-hours, kilowatt-hours, electronvolts, BTU, therms, foot-pounds, ergs, and tons of TNT. One input fills a full table, so you can compare a food label, an electricity bill, and a gas bill in the same unit.
Common energy units
| Unit | Joules |
|---|---|
| 1 calorie (cal) | 4.184 |
| 1 kilocalorie (kcal) | 4,184 |
| 1 BTU (IT) | 1,055.056 |
| 1 watt-hour (Wh) | 3,600 |
| 1 kilowatt-hour (kWh) | 3,600,000 |
| 1 therm (US) | 105,480,400 |
| 1 electronvolt (eV) | 1.602 × 10⁻¹⁹ |
Practical examples
- Nutrition: a 2,000 kcal daily diet equals 8,368 kJ, or about 2.32 kWh – roughly what a dishwasher uses in two cycles.
- Heating: gas is often billed in therms or kWh. One US therm is about 29.3 kWh, so comparing a gas quote with an electric heat pump quote becomes straightforward.
- Air conditioning: equipment rated in BTU can be compared with electrical energy – 1 kWh is about 3,412 BTU.
- Physics: particle and photon energies are quoted in electronvolts. Visible light photons carry roughly 1.6–3.3 eV.
Energy vs. power
Energy is the total amount of work done; power is the rate at which it is done. Kilowatt-hours are energy, kilowatts are power. If you have a power rating and want the energy used over time, multiply by the hours first, or use the Power Converter to switch power units.
Accuracy
All factors are exact definitions where they exist (calorie, watt-hour, electronvolt since the 2019 SI redefinition) and the International Table value for the BTU. Pick up to 10 decimals, and very small values such as electronvolt results switch to scientific notation automatically. For temperature-related calculations try the Temperature Converter.
Frequently Asked Questions
How many kilojoules are in a calorie?
A food Calorie (kilocalorie) is 4.184 kJ. A small thermochemical calorie is 4.184 J. Food labels that say 'Calories' or 'kcal' mean the kilocalorie.
How many BTU are in a kilowatt-hour?
One kilowatt-hour is about 3,412.14 BTU (International Table BTU), and one BTU is about 1.055 kJ.
What is the difference between kW and kWh?
kW is power – how fast energy is used. kWh is energy – power multiplied by time. A 2 kW heater running for 3 hours uses 6 kWh.
Which calorie does the converter use?
The thermochemical calorie, defined as exactly 4.184 joules, and the kilocalorie (food Calorie) as 4,184 joules.