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Energy
Energy Converter
Convert joules, calories, kWh, BTU, and more
Conversion Formula
Target = Value × (From Ratio / To Ratio)
Energy conversions use linear ratios. Target = Value × (Source Ratio / Target Ratio). To convert joules to calories: multiply by 1 / 4.184.
Energy conversion is essential in physics, nutrition, and engineering. Convert between joules, calories, kilowatt-hours, BTUs, and electronvolts.
Food energy is typically measured in kilocalories (often just called 'Calories' with a capital C). One food Calorie equals 4,184 joules.
All Supported Energy Units
| Unit | Symbol | Definition |
|---|---|---|
| Joule | J | The SI unit of energy, defined as 1 newton-meter. |
| Kilojoule | kJ | One thousand joules, used for nutritional energy labeling. |
| Megajoule | MJ | One million joules, used for large-scale energy measurements. |
| Calorie | cal | The energy needed to raise 1 gram of water by 1°C. |
| Kilocalorie | kcal | One thousand calories, the unit used for food energy labeling. |
| Watt-hour | Wh | The energy delivered at 1 watt for 1 hour. |
| Kilowatt-hour | kWh | One thousand watt-hours, the standard unit for electricity billing. |
| British Thermal Unit | BTU | The energy needed to raise 1 pound of water by 1°F, used in HVAC. |
| Electronvolt | eV | The energy gained by an electron accelerating through 1 volt. |
| Erg | erg | The CGS unit of energy, used in astrophysics and mechanics. |
| Foot-pound | ft-lb | The imperial unit of energy, the work done by 1 pound-force over 1 foot. |
Common Energy Conversions
| From | To | Value |
|---|---|---|
| 1 J | cal | 0.239 |
| 1 kcal | kJ | 4.184 |
| 1 kWh | J | 3,600,000 |
| 1 BTU | J | 1,055 |
Frequently Asked Questions
A lowercase 'calorie' (cal) is 4.184 joules. A food 'Calorie' (kcal) is 1,000 calories or 4,184 joules. Food labels use Calories (with capital C) meaning kilocalories.
An electronvolt (eV) is the energy gained by a single electron accelerating through 1 volt. It is tiny (1.6 × 10⁻¹⁹ J) and used in particle physics.
To convert joules to calories, divide by 4.184. For example, 418.4 J ÷ 4.184 = 100 calories. This is useful for comparing mechanical and food energy.
A kilowatt-hour (kWh) is 3.6 million joules. It is the standard unit for electricity billing — if a 1,000 W appliance runs for 1 hour, it uses 1 kWh.
One kilocalorie (food Calorie) equals exactly 4,184 joules or 4.184 kJ. This is the standard conversion for food energy to mechanical energy.
BTU (British Thermal Unit) is primarily used in heating, ventilation, and air conditioning (HVAC) to measure thermal energy. One BTU is the energy to raise 1 lb of water by 1°F.
One watt-hour (Wh) equals 3,600 joules. To convert Wh to J, multiply by 3,600. To convert kWh to J, multiply by 3,600,000.