⚡ Energy Converter
Convert between joules, calories, kilowatt-hours, BTU and more.
What is this tool?
The Energy Converter is a free online tool that instantly converts between all common units of energy. From physics homework to nutrition labels to electricity bills, energy is expressed in many different units depending on the context, and this converter bridges them all with precision. Energy is the capacity to do work, and the SI unit is the joule (J). One joule is a small amount of energy — roughly the energy needed to lift a small apple one meter. In nutrition, calories (cal) and kilocalories (kcal, often written as Calories with a capital C) measure the energy content of food. In electricity, kilowatt-hours (kWh) are the standard billing unit for power consumption. The British Thermal Unit (BTU) is used for heating and cooling systems. Electron-volts (eV) describe energy at the atomic scale in physics. This converter handles joules, kilojoules, calories, kilocalories, watt-hours, kilowatt-hours, BTU, and electron-volts. Simply enter a value in any field and all other fields update instantly. Everything runs locally in your browser.How it works
The converter uses the joule as the common base unit. All conversions first go to joules, then from joules to every other unit. The key conversion factors are: 1 kilojoule (kJ) = 1,000 J; 1 thermochemical calorie (cal) = 4.184 J; 1 kilocalorie (kcal) = 4,184 J; 1 watt-hour (Wh) = 3,600 J; 1 kilowatt-hour (kWh) = 3,600,000 J; 1 BTU = 1,055.06 J; 1 electron-volt (eV) = 1.60218 × 10⁻¹⁹ J. A common source of confusion is the difference between calories and kilocalories. Nutrition labels use Calories (capital C), which are actually kilocalories — 1 Calorie = 1 kcal = 1,000 calories. The converter clearly labels both to avoid mistakes. Another important distinction is between different BTU definitions; this tool uses the International Table BTU (1 BTU = 1055.06 J), which is the most common standard. All calculations use JavaScript double-precision arithmetic. For the extremely small numbers involved in electron-volts, the converter maintains full precision across the entire range.How to use
- Enter an energy value in any field.
- All other fields update automatically.
- Be mindful of calories vs kilocalories.
- Copy any result with one click.
- Use clear to reset all fields.
Frequently Asked Questions
Frequently Asked Questions
What is the difference between calories and kilocalories?
A small calorie (cal) is the energy to heat 1 gram of water by 1°C. A kilocalorie (kcal) is 1,000 calories. Food labels use Calories with a capital C, which are actually kilocalories. 1 Calorie = 1 kcal = 4,184 joules.
How do I convert kWh to joules?
One kilowatt-hour equals 3,600,000 joules (3.6 MJ). This is because 1 watt = 1 joule/second, and there are 3,600 seconds in an hour. So 1 kWh = 1000 W × 3600 s = 3,600,000 J.
What is a BTU and where is it used?
BTU (British Thermal Unit) is the energy needed to heat one pound of water by one degree Fahrenheit. It is widely used in HVAC (heating, ventilation, and air conditioning) systems, especially in North America. 1 BTU ≈ 1055 joules.
What is an electron-volt?
An electron-volt (eV) is the energy gained by an electron moving through 1 volt of potential difference. It is used in atomic and particle physics because the joule is too large a unit for those scales. 1 eV ≈ 1.602 × 10⁻¹⁹ joules.
Tips & Advice
The most common energy conversion mistake is confusing calories with kilocalories. On nutrition labels, Calorie (capital C) means kilocalorie. When comparing energy in food versus energy in electricity, note that 1 kcal is about 0.00116 kWh — a typical adult needs about 2,000 kcal per day, which is roughly 2.3 kWh. For HVAC work, remember that BTU ratings describe cooling or heating capacity per hour. When working with very small energies in physics, scientific notation is essential. This converter handles the full range from electron-volts to kilowatt-hours without losing precision.