Energy Converter
Convert between all 8 energy units — Joule, Kilojoule, Calorie, Kilocalorie, Watt Hour, Kilowatt Hour, British Thermal Unit, Foot-Pound — with instant results, formulas and worked examples.
A single converter for every energy unit on ConvertWorks. Pick any two units, type a value, and get an instant, accurate result — no page reloads and nothing leaves your browser. Dedicated pages for the most popular pairs are linked below.
Quick reference — Joules to Kilojoules
Every unit above is defined relative to the joules: pick any pair and the converter divides the two base factors, so results stay consistent across the whole category.
How to use this calculator
- Choose the unit you have in the From dropdown.
- Choose the unit you want in the To dropdown.
- Type your value — the result updates instantly.
- Use Swap to reverse the conversion, or open a dedicated pair page below for one specific conversion.
The formula
Result = Value × (from-unit factor ÷ to-unit factor), with all factors relative to the joules.
Worked example
100 cal = 418.4 J — in full, 100 Calories converts to 418.4 Joules. Food energy, electricity bills and heating are the everyday jobs for this conversion.
Frequently Asked Questions
What units does this energy converter include?
It covers Joule, Kilojoule, Calorie, Kilocalorie, Watt Hour, Kilowatt Hour, British Thermal Unit, Foot-Pound — 8 units in total. Every conversion runs through the joules as the common reference, so any pair you pick stays consistent with every other pair.
How does this energy converter work?
Each unit is defined by an exact factor relative to the joules. To convert, the tool multiplies your value by the from-unit's factor and divides by the to-unit's factor, then rounds the display to six significant figures.
How accurate are the results?
The factors come from the official definitions of the units (for example, 1 inch is exactly 0.0254 meters and 1 pound is exactly 0.45359237 kilograms), so conversions are as accurate as the definitions themselves. Display rounding to six significant figures can hide trailing digits on extreme values.
Can I convert Calories to Joules with this tool?
Yes — select Calories and Joules in the dropdowns. For example, 100 Calories equals 418.4 Joules, and the dedicated pair page linked below focuses on just that conversion.