Energy Converter
Convert between joules, calories, kcal, kWh, BTU and electronvolts with real-world energy references
All Conversions
J
4184.000
cal
1000.001
kcal
1.000
kWh
0.001
BTU
3.966
eV
2.61e+22
Common Energy References
Energy in 1 food calorie (kcal)
4.18e+3 J
Energy in 1 kWh
8.40e+6 J
Energy in 1 BTU
1.06e+3 J
Daily diet (2000 kcal)
7.50e+6 J
Energy to boil 1L of water
2.26e+6 J
Kinetic energy of 1-tonne car at 100 km/h
3.60e+6 J
Energy in 1 ton of TNT
4.18e+9 J
Energy Units
- J (joule): SI unit of energy
- cal/kcal: calories (food energy, 1 food calorie = 1 kcal)
- kWh: kilowatt-hour (electricity billing)
- BTU: British Thermal Unit (heating/cooling)
- eV: electron volt (particle physics)
Energy Units
Energy (work, heat) in many units: joule (J, SI base), calorie (cal), kilocalorie (kcal, food calories), British Thermal Unit (BTU), kilowatt-hour (kWh), electronvolt (eV). Convert: 1 kcal = 4,184 J = 3.97 BTU. 1 kWh = 3,600,000 J = 3,412 BTU = 860 kcal.
Reference values: human daily food intake = 2,000-2,500 kcal = 8.4-10.5 MJ. Light bulb hour = 60 Wh = 216,000 J = 51.6 kcal. Petrol energy = 9.7 kWh per litre = 35 MJ/L. UK household annual electricity = 2,900 kWh average. Lithium battery: ~265 Wh/kg energy density.
Common Energy Conversions
| From | To |
|---|---|
| 1 J | 0.000239 cal |
| 1 kcal (food) | 4,184 J |
| 1 BTU | 1,055 J |
| 1 kWh | 3,600,000 J |
| 1 kWh | 3,412 BTU |
| 1 kWh | 860 kcal |
| 100 kcal (banana) | 418 kJ |
| 1 MJ | 0.278 kWh |
Frequently Asked Questions
What's the difference between energy and power?
Power is rate of energy use (W, kW). Energy is total work done (J, kWh). A 1 kW heater running 1 hour uses 1 kWh of energy. A 100 W bulb running 10 hours = same 1 kWh. Watt is rate; kWh is amount.
How is this useful in real life?
Comparing food labels (UK kcal vs Australian kJ). Energy bills (kWh = unit charged for electricity). Heating cost calculations. Electric vehicle range (kWh battery × Wh/km efficiency). Investment in solar (kWh/year output relative to consumption).