Energy Converter
Convert energy between joules, kilojoules, calories, kilocalories, watt-hours, kilowatt-hours, BTU, electronvolts, foot-pounds, therms, and more. Instant, accurate, and completely private — everything runs in your browser.
Common energy conversions
| From | To | Factor |
|---|---|---|
| 1 Joule | Calories | 0.239006 cal |
| 1 Calorie | Joules | 4.184 J |
| 1 Kilocalorie (food cal) | Kilojoules | 4.184 kJ |
| 1 Watt-hour | Joules | 3,600 J |
| 1 Kilowatt-hour | Megajoules | 3.6 MJ |
| 1 BTU | Joules | 1,055.06 J |
| 1 Electronvolt | Joules | 1.602 × 10⁻¹⁹ J |
| 1 Foot-pound | Joules | 1.35582 J |
| 1 Therm | Joules | 105.506 MJ |
Why use this energy converter?
Energy units are used everywhere — from nutrition labels and electricity bills to physics homework and engineering specs. The problem is that there are dozens of units, and converting between them manually is error-prone. This tool does it instantly and accurately.
- Wide unit coverage — joules, calories, kWh, BTU, eV, therms, and more.
- Instant results — conversions happen as you type.
- Precise factors — uses exact SI definitions and standard conversion constants.
- 100% private — nothing is sent to any server.
- Works offline — after the page loads, it works without internet.
How to use the energy converter
1. Enter a value
Type the number you want to convert. Decimals and negative values are supported.
2. Pick units
Choose the "From" and "To" units. Use the swap button to flip them instantly.
3. Get the result
The converted value appears instantly. No need to click — it updates as you type.
Energy units explained
| Unit | Symbol | Common use |
|---|---|---|
| Joule | J | SI unit of energy. Used in physics and engineering. |
| Kilojoule | kJ | Food energy labels in many countries. |
| Calorie | cal | Small calorie — energy to heat 1g of water by 1°C. |
| Kilocalorie | kcal | Food Calorie — 1,000 small calories. |
| Watt-hour | Wh | Electrical energy — 1 watt for 1 hour. |
| Kilowatt-hour | kWh | Electricity billing unit. |
| BTU | BTU | British Thermal Unit — heating and cooling. |
| Electronvolt | eV | Atomic and particle physics. |
| Foot-pound | ft·lb | Torque and mechanical energy (US). |
| Therm | thm | Natural gas billing. |
| Erg | erg | CGS unit of energy. |
| Ton of TNT | tTNT | Explosive energy comparison. |