Free Energy Converter – Convert Joules, Calories & kWh
Convert between joules, calories, kilowatt-hours and BTU.
About the Energy Converter
What is the Energy Converter?
An energy converter translates energy values between joules, calories, watt-hours and British thermal units.
Why use this calculator?
Nutrition labels use calories, electricity bills use kilowatt-hours, and heating systems use BTUs, so a single converter ties them together.
How to use it
- Enter the energy value.
- Choose the source and target units.
- Read the converted energy.
Formula
One caloric (food) calorie is 1 kilocalorie, equal to 4,184 joules.
One kilowatt-hour is 3.6 million joules, the energy of a 1,000 W appliance running for one hour.
Frequently Asked Questions
Is a food calorie the same as a physics calorie?
No. A food (large) calorie is 1,000 physics (small) calories, or one kilocalorie.
How many joules is a kilowatt-hour?
Exactly 3,600,000 joules.
How precise are the conversions?
Conversions use standard, internationally defined factors and are rounded for display. They are accurate to the number of digits shown.
Can I convert back and forth without losing accuracy?
Yes. Enter the original value to get an exact inverse conversion; avoid chaining rounded results if you need maximum precision.
Which measurement system is used?
Both metric (SI) and US customary / imperial units are supported and clearly labelled.
Is this calculator free to use?
Yes. Every calculator on this site is completely free, with no hidden fees, no subscriptions and no limits on how many times you can use it.
How accurate are the results?
We use standard, widely accepted formulas and calculate in your browser using double-precision arithmetic. Results are rounded for readability, so treat them as reliable estimates rather than a guarantee. Real-world factors can vary the true figure.
Can I add this calculator to my own website?
Yes. Open this calculator page and use the "Add to your website" box in the sidebar to copy a ready-made iframe snippet, then paste it into any HTML page.
Does it work on a phone or tablet?
Yes. The layout is fully responsive, so it works on desktops, laptops, tablets and mobile phones, and every input adapts to touch screens.
Is the information I type kept private?
Yes. All calculations run locally in your browser. Nothing you enter is uploaded, stored or shared with anyone.