Energy Unit Converter
Convert between every energy unit in one place. Pick any two units, see the exact factor and the worked calculation.
How to use it
- Choose the unit you have and the unit you want.
- Type a value — the conversion is instant and shows the working underneath.
- Swap flips the two units. The URL always reflects what you see.
This converter covers every common energy unit in one page rather than one fixed pair, so you are not hunting for a specific "X to Y" page when the two units you need are not the ones most people search for.
Pick the unit you have, the unit you want, and type a value — the result and the conversion factor both update immediately, worked out to full precision rather than a rounded rule of thumb.
Energy units on this page
| Unit | Symbol | Notes |
|---|---|---|
| Joule | J | Physics, mechanical work and food energy in most of the world. |
| Kilojoule | kJ | Nutrition labels outside the US, and heating calculations. |
| Megajoule | MJ | Fuel energy content and industrial process heat. |
| Gigajoule | GJ | Commercial gas billing and district heating. |
| Calorie (small) | cal | Chemistry and physics. Note this is the small calorie, not the food one. |
| Kilocalorie (food Calorie) | kcal | Nutrition and diet planning. |
| Watt-hour | Wh | Battery capacity for laptops, phones and power banks. |
| Kilowatt-hour | kWh | Electricity billing everywhere, and EV battery capacity. |
| British thermal unit | BTU | Heating, air conditioning and gas in the US. |
| Electronvolt | eV | Atomic and particle physics, and semiconductor band gaps. |
| Kiloelectronvolt | keV | X-ray energies and electron microscopy. |
| Megaelectronvolt | MeV | Nuclear physics and radiation therapy. |
A worked example
1 J = 0.00027777778 Wh. That factor comes from each unit's fixed relationship to the dimension's base unit — nothing here is approximated or looked up from a rounded table.
Every pairing on this page uses the same approach, so a chain of conversions (say, millimetres to miles) stays accurate rather than compounding rounding error the way repeated approximate factors would.
Everything runs in your browser
There is no server involved in the calculation. The numbers you type never leave your device, nothing is logged, and the page keeps working with no connection once it has loaded. That is not a marketing line — it is simply how the tool is built, because a calculation like this has no reason to touch a network.
Last updated 18 August 2026