Free online energy converter
Energy is measured by field — joules in physics, kilocalories in nutrition, kilowatt-hours on your electricity bill, BTU in heating. This converter handles all of them.
Result
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All units
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How to use
- Enter the energy value you want to convert.
- Select the unit you are converting from.
- Select the unit you want the result in.
- The converted value appears instantly, and the table below shows equivalents in all supported units.
Conversion reference
| From | To | Multiply by |
|---|---|---|
| kWh | Joules | 3,600,000 |
| kWh | kJ | 3,600 |
| kWh | BTU | 3,412.14 |
| kcal | Joules | 4,184 |
| kcal | kJ | 4.184 |
| BTU | Joules | 1,055.06 |
| BTU | kWh | 0.000293071 |
| cal | Joules | 4.184 |
Note: calories here are thermochemical calories (cal = 4.184 J exactly). Food/nutrition calories are kilocalories (kcal).
Energy in context
| Energy amount | Equivalent |
|---|---|
| 1 food calorie (kcal) | 4,184 joules |
| 1 kWh (electricity) | 3,600 kJ = 3,412 BTU |
| Typical household monthly use | ~900 kWh = 3,240 MJ |
| 1 BTU | Energy to raise 1 lb water by 1°F |
| Bolt of lightning | ~1 GJ (rough estimate) |
Worked examples
A 40 W LED light bulb, 6 hours a day for a month
- Daily energy: 40 W × 6 h = 240 Wh = 0.24 kWh/day
- Monthly: 0.24 × 30 = 7.2 kWh
- At $0.15/kWh: about $1.08/month
Walking off a 500-kcal meal
- 500 kcal × 4,184 J/kcal = 2,092,000 J (2.09 MJ)
- Walking burns roughly 300 kcal/hour at brisk pace → ~1 h 40 min
- Same 500 kcal = 0.581 kWh (the energy to run an LED bulb for 14 hours)
Air conditioner sizing — 12,000 BTU/hour AC
- 12,000 BTU = 12,000 × 1,055.06 = 12.66 MJ/hour
- In electric terms: 12,000 × 0.000293071 = 3.52 kWh/hour of heat removal
- The AC itself draws less (maybe 1.1 kW) because it moves heat, it doesn’t generate it.
Notes
- Calorie confusion — nutrition labels say “calories” but mean kilocalories (kcal). A 200-calorie snack is 200 kcal = 200,000 cal = 836,800 J. The converter uses the technical definitions; when in doubt about food labels, treat “Cal” with a capital C as kcal.
- Electronvolt conversions involve very large or very small numbers; the converter uses scientific notation automatically.
- Calorie values follow the thermochemical definition (1 cal = 4.184 J) used in chemistry and physics, not the international table calorie (4.1868 J).
- Results are rounded to 6 significant figures.
Frequently asked
How many joules are in a kilowatt-hour?
1 kilowatt-hour = 3,600,000 joules (3.6 megajoules). A kilowatt-hour is the energy used by a 1,000-watt device running for one hour.
What is the difference between a calorie and a kilocalorie?
A small calorie (cal) is the energy needed to raise 1 gram of water by 1°C. A kilocalorie (kcal) is 1,000 small calories. Food calories listed on nutrition labels are kilocalories — so 200 food calories = 200 kcal = 200,000 cal.
How do you convert BTU to kilowatt-hours?
1 BTU = 0.000293071 kWh. To convert kWh to BTU, multiply by 3,412.14. BTU (British Thermal Unit) is the heat needed to raise 1 pound of water by 1°F.
How many joules are in a kilocalorie?
1 kcal = 4,184 joules. This is the thermochemical definition used in nutrition.
What is an electronvolt?
An electronvolt (eV) is the energy gained by one electron moving through 1 volt of electric potential — about 1.602 × 10^-19 joules. It is used in atomic and particle physics.
How do I read my electricity bill in joules?
Multiply kilowatt-hours by 3,600,000. A typical US household uses about 900 kWh per month — roughly 3.24 × 10^9 joules (3.24 gigajoules).