Energy Converter — Joules, Calories, kWh, BTU & More
Convert between joules, calories, kilowatt-hours, BTUs, electronvolts, and more. Free online energy unit converter for physics, nutrition, and engineering.
Energy Converter
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The Formula
Energy conversion uses linear factors relative to the Joule (J), the SI base unit of energy. Each unit is converted to Joules first, then divided by the target unit's Joule factor. For example, converting 1 kWh to BTU: 1 kWh × 3,600,000 J/kWh ÷ 1055.06 J/BTU = 3412.14 BTU.
Variable Definitions
Energy
The capacity to do work, measured in joules (SI) or various derived units for specific contexts.
One Joule
The energy transferred when a one-newton force moves an object one meter. The SI base unit of energy.
One Kilowatt-Hour
The energy consumed by a 1,000-watt device running for one hour. Equal to 3.6 million joules. The standard unit for electricity billing.
One Calorie
The energy needed to raise one gram of water by 1°C. Food Calories (kcal) are 1,000 times larger.
One British Thermal Unit
The energy to raise one pound of water by 1°F. Used for HVAC, heating systems, and natural gas. 1 BTU ≈ 1,055 J.
How to Use This Calculator
- 1
Enter the energy value you want to convert in the "Value" field.
- 2
Select the current energy unit from the "From" dropdown.
- 3
Select the desired energy unit from the "To" dropdown.
- 4
The converted value is displayed instantly along with the conversion formula.
- 5
Check the common uses section for real-world energy comparisons — like how many kWh a home uses or the energy content of gasoline.
Quick Reference
| From | To |
|---|---|
| 1 kWh | 3.6 MJ / 3,412 BTU |
| 1 BTU | 1.055 kJ / 0.000293 kWh |
| 1 cal | 4.184 J |
| 1 food Cal (kcal) | 4.184 kJ |
| 1 therm | 105.5 MJ / 29.3 kWh |
| 1 eV | 1.602 × 10⁻¹⁹ J |
| 1 ft·lb | 1.356 J |
| 1 TCE | 29.3 GJ / 8,141 kWh |
Common Applications
- Average US home: ~900 kWh/month (30 kWh/day)
- EV battery: 50–100 kWh for 200–350 miles of range
- Gasoline: 33.7 kWh per gallon of energy content
- Human daily food energy: ~2,000 kcal (8.37 MJ)
- AC unit: 12,000 BTU/h (3.5 kW) cools ~500 sq ft
- Light bulb: 10 W LED running 100 hours = 1 kWh
Energy converts between forms; the total energy is always conserved
Understanding the Concept
Energy exists in many forms — mechanical, electrical, thermal, chemical, and nuclear — and each field has developed its own preferred units. Physicists use joules (J), the SI unit. Electricity bills measure consumption in kilowatt-hours (kWh). Food energy is labeled in kilocalories (kcal) or Calories. Heating and cooling systems use BTUs. Chemistry and particle physics use electronvolts (eV). Natural gas is measured in therms, and coal energy in tonnes of coal equivalent (TCE). Understanding energy conversions is essential for comparing energy costs, evaluating appliance efficiency, calculating exercise calorie burn, and understanding climate and energy policy. For example, one gallon of gasoline contains about 33.7 kWh of energy, while an average US home uses about 900 kWh per month. A single calorie (food Calorie, technically a kilocalorie) can raise the temperature of one kilogram of water by 1°C.
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