Convert joules, kilojoules, kilowatt-hours, watt-hours, BTU, calories, kcal, electronvolts, ergs, foot-pounds, therms and TNT energy equivalents.
Energy units appear in physics, electricity bills, HVAC, nutrition, chemistry, mechanics and explosive-yield comparisons. This converter uses the joule as the base unit, then reports the selected conversion plus practical reference outputs for kWh, kcal, BTU, electronvolts and TNT equivalent.
1 joule equals 1 joule.
All conversions pass through joules.
Used for electrical energy billing.
Thermochemical kcal, common in nutrition.
International Table BTU for engineering.
Useful for atomic and particle scale energy.
Energy Conversion Formulas
The joule (J) is the SI derived unit of energy, work and heat. This calculator converts the source value into joules first, then divides by the target unit factor. That keeps electrical, thermal, mechanical and atomic-scale conversions consistent.
energy in joules = input value x source unit factor
target value = energy in joules / target unit factor
1 W s = 1 J
1 Wh = 3600 J, so 1 kWh = 3,600,000 J
1 thermochemical calorie = 4.184 J, so 1 kcal = 4184 J
1 electronvolt = 1.602176634 x 10^-19 J
1 ton TNT equivalent = 4.184 x 10^9 J
Physics and Mechanics
Use joules, kilojoules, megajoules, foot-pound-force and horsepower-hour for work, kinetic energy, potential energy and mechanical output.
Electricity
Use watt-hours, kilowatt-hours and megawatt-hours for electrical consumption. A kilowatt-hour is energy, not power: 1 kWh = 3.6 MJ.
Heat and Nutrition
Use calories, kilocalories, BTU and therms for heat, food energy, HVAC and fuel billing. Be clear whether calorie means small calorie or food Calorie.
Atomic Scale
Use electronvolts, keV, MeV, GeV, TeV, Hartree and Rydberg for atomic, quantum, nuclear and particle physics calculations.
Common Energy Conversion Table
Use this table for quick reference. The calculator keeps more precision internally and formats large or tiny values using scientific notation when needed.
| Unit | Symbol | Value in joules | Typical use |
|---|---|---|---|
| Joule | J | 1 J | SI unit of energy, work and heat |
| Kilojoule | kJ | 1000 J | Food labels, chemistry and physics examples |
| Megajoule | MJ | 1,000,000 J | Fuel, heat and large mechanical energy |
| Watt-hour | Wh | 3600 J | Battery and electrical energy |
| Kilowatt-hour | kWh | 3,600,000 J | Electricity bills and appliance use |
| Thermochemical calorie | cal th | 4.184 J | Heat and chemistry reference unit |
| Thermochemical kilocalorie | kcal th | 4184 J | Food energy and nutrition calculations |
| British thermal unit, IT | BTU IT | 1055.05585262 J | HVAC and heat engineering |
| Electronvolt | eV | 1.602176634 x 10-19 J | Atomic, nuclear and particle energy |
| Erg | erg | 1 x 10-7 J | CGS mechanics and older physics references |
| Foot-pound-force | ft lbf | 1.3558179483314004 J | Mechanical work and torque-adjacent calculations |
| Ton of TNT equivalent | ton TNT | 4.184 x 109 J | Explosive-yield and large-event comparison |
Worked Energy Conversion Examples
Example 1: kWh to joules
Problem: Convert 2.5 kWh to joules.
Method: 1 kWh = 3,600,000 J, so 2.5 x 3,600,000 = 9,000,000 J.
Example 2: kcal to kJ
Problem: Convert 500 kcal to kilojoules.
Method: 500 kcal x 4184 J = 2,092,000 J. Divide by 1000 to get 2092 kJ.
Example 3: BTU to kWh
Problem: Convert 12,000 BTU IT to kWh.
Method: 12,000 x 1055.05585262 J = 12,660,670.23144 J. Divide by 3,600,000 to get 3.51685 kWh.
Example 4: joules to electronvolts
Problem: Convert 1 microjoule to eV.
Method: 1 microjoule = 1 x 10-6 J. Divide by 1.602176634 x 10-19 J/eV to get about 6.241509 x 1012 eV.
How to Choose the Right Energy Unit
Energy spans a very large range. The same base quantity can describe the energy in a single electron transition, a snack, a household electricity bill, a vehicle fuel reserve, an HVAC load or an explosive-yield comparison. Choosing the right unit makes the result easier to read and reduces mistakes.
Use joules for science
Joules, kilojoules and megajoules are the cleanest choices for physics, chemistry and engineering because they connect directly with SI units.
Use kWh for electricity
Electricity suppliers normally bill energy in kilowatt-hours. A 1500 W heater running for 2 hours uses 3 kWh.
Use kcal for food energy
Food labels often use Calories with a capital C. In nutrition, 1 Calorie is 1 kilocalorie, about 4184 joules.
Use BTU for HVAC
BTU is common in heating, cooling and fuel discussions. Make sure the context specifies BTU per hour when the value is a power rating.
Use eV for particles
Electronvolts make tiny atomic and particle energies readable. Joules are still the SI base reference, but eV avoids very small decimals.
Use TNT units carefully
TNT equivalent is a comparison scale, not a general engineering energy unit. Use it only when large releases or yield comparisons are the topic.
Common Mistakes in Energy Conversion
- Mixing energy and power: kW is power, while kWh is energy. A device rated at 1 kW uses 1 kWh only after running for 1 hour.
- Confusing calories and Calories: a food Calorie is a kilocalorie, so 1 Cal = 1000 small calories.
- Using BTU/h as BTU: BTU is energy, while BTU per hour is power. HVAC ratings commonly use BTU/h.
- Rounding too early: convert with full precision first, then round the final answer to the precision needed for the task.
- Forgetting context-specific calorie and BTU variants: IT, thermochemical and mean definitions differ slightly. Use the variant specified by the problem or standard.
Related RevisionTown Energy Tools
Use these related pages when you need a narrower converter, a physics calculator or a supporting energy unit explanation:
- Energy conversion calculators
- Energy converter
- Joules to kWh conversion
- kWh to joules conversion
- Calories to joules conversion
- kJ to BTU conversion
- BTU to kJ conversion
- Potential energy calculator
Data Sources and Precision Notes
This converter uses joules as the base unit. Common engineering and thermal conversion factors follow NIST SP 811 conversion tables, while electronvolt, Hartree and Rydberg energy factors follow NIST CODATA constants. Approximate energy-economics units are clearly marked in the unit names.
- 1 kWh = 3.6 x 106 J and 1 Wh = 3600 J.
- 1 electronvolt = 1.602176634 x 10-19 J, exact in the modern SI.
- 1 thermochemical calorie = 4.184 J and 1 thermochemical kilocalorie = 4184 J.
- 1 BTU IT = 1055.05585262 J; BTU variants differ slightly.
- 1 erg = 1 x 10-7 J and 1 foot-pound-force = 1.3558179483314004 J.
- 1 ton TNT equivalent = 4.184 x 109 J.
