Energy Converter
Convert between energy units — joules, kilojoules, calories, kilocalories, watt-hours and more.
Reviewed by the ToolNestr Editorial Team — July 2026
About this energy converter
Energy is the capacity to do work, measured in joules, calories and kilowatt-hours. This energy converter lets you move between 8 different energy units in either direction. Pick the unit you are starting from, the unit you want, and enter a value — the result appears instantly as you type, with the calculation running entirely in your browser.
Internally, every unit is defined by its exact ratio to a single base unit, the joule. To convert, the tool first changes your value into the base unit, then into the target unit. This base-unit method keeps results consistent and precise no matter which pair of units you choose, and makes it easy to add uncommon units alongside the everyday ones.
Use the swap control to reverse the direction at any time, which is handy when you are checking a figure both ways. Because the converter is mobile-first and works offline once loaded, it is a quick reference for energy whether you are studying, working, travelling or shopping across measurement systems.
Supported energy units
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Frequently asked questions
How does this energy converter work?
Choose the unit you have and the unit you want, type a value, and the tool converts it via a common base unit (the joule). It supports 8 energy units.
Is the energy converter accurate?
Yes. Every unit is defined by its exact ratio to the joule, so conversions are precise; displayed results are rounded for readability.
Can I convert in both directions?
Yes. Swap the “from” and “to” units, or press the swap button, to convert either way between any two energy units.
Which energy units are supported?
It includes Joules, Kilojoules, Calories, Kilocalories, Watt-hours, Kilowatt-hours, British thermal units, Foot-pounds.