Energy Unit Converter
Convert between various energy units with precision and ease
Scientific Note: This converter uses standard conversion factors for energy units. For scientific applications requiring extreme precision, please refer to the latest CODATA internationally recommended values for fundamental physical constants.
Tip: For best results, enter your value using scientific notation for very large or small numbers (e.g., 1.5e6 for 1,500,000).
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Conversion Formulas
Common Energy Equivalents
Understanding Energy Units
Scientific Energy Units
- Joule (J): The SI unit of energy, work, and heat
- Kilojoule (kJ): 1,000 joules, common in food energy
- Electron Volt (eV): Energy gained by an electron moving across 1 volt
- Mega Electron Volt (MeV): Used in nuclear physics
Dietary and Thermal Energy
- Calorie (cal): Energy to raise 1g of water by 1°C
- Kilocalorie (kcal): Food Calories (capital C)
- BTU: British Thermal Unit, used in HVAC systems
- Therm: Approximately 100,000 BTU, used for gas billing
Electrical and Mechanical Energy
- Kilowatt-hour (kWh): Energy used by 1kW power for 1 hour
- Watt-hour (Wh): Used for smaller electrical energy measurements
- Foot-pound (ft·lb): Work done by 1 pound of force over 1 foot
- Erg: A very small unit equal to 10^-7 joules
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Energy in Everyday Life
Food Energy
The energy content in food is typically measured in kilocalories (kcal), often labeled as "Calories" with a capital C on food packaging. An average adult needs about 2,000-2,500 kcal per day. A single gram of carbohydrates provides about 4 kcal, protein provides 4 kcal, and fat provides 9 kcal.
Household Energy
Electricity usage in homes is measured in kilowatt-hours (kWh). A typical US household uses about 900 kWh per month. Running a 100-watt light bulb for 10 hours consumes 1 kWh. Natural gas for heating is often billed in therms, with each therm containing approximately 100,000 BTU of heat energy.
Energy in Physics
In physics and chemistry, joules are the standard unit. A single joule is approximately the energy needed to lift an apple one meter against Earth's gravity. In quantum physics, electron volts (eV) are common, with chemical bonds typically having energies of a few eV, while nuclear reactions involve millions of eV (MeV).
Pro Tip: When working across scientific disciplines, it's often easiest to convert everything to joules (the SI unit) for calculations, and then convert back to your preferred unit for the final result.
Frequently Asked Questions
What's the difference between a calorie and a Calorie?
A small "calorie" (cal) is the amount of energy needed to raise 1 gram of water by 1°C. A large "Calorie" (Cal) with a capital C, also called a kilocalorie (kcal), equals 1,000 small calories. Food labels typically use Calories/kilocalories when stating nutritional information, though they often just write "calories" on packaging.
Why are there so many different energy units?
Different energy units evolved in various scientific and practical contexts. Joules became the standard SI unit, but older units persist in specific fields: calories in nutrition, BTUs in heating systems, kilowatt-hours in electricity, and electron volts in atomic physics. Each unit is scaled appropriately for its typical application, making calculations more convenient in that field.
How accurate are these energy conversions?
This calculator uses standard conversion factors that are accurate to many decimal places. For most practical purposes, these conversions are more than sufficient. However, some definitions (especially for units like the calorie) have varied slightly throughout history. For extremely precise scientific work, we recommend referencing the latest CODATA values and specifying exactly which definition you're using.
Why is energy measured in watt-hours for electricity?
While joules are the standard unit of energy, the electrical industry adopted watt-hours (Wh) and kilowatt-hours (kWh) because they relate directly to power usage over time. Since many electrical devices are rated in watts (power), multiplying this by the usage time gives energy consumption in watt-hours. One kilowatt-hour equals 3.6 million joules, which would be unwieldy for billing purposes.
How is energy different from power?
Energy is the capacity to do work, measured in units like joules or kilowatt-hours. Power is the rate at which energy is transferred or converted, measured in watts (joules per second). Think of energy as the total amount of water in a tank, while power is how quickly that water flows out. A 100-watt light bulb uses 100 joules of energy every second it's on.