Convert energy between joules, kilojoules, calories, kilocalories (food calories), watt-hours, kilowatt-hours, and British thermal units (BTU). Energy appears on food labels, electricity bills, heating specs, and physics problems, each with its own favored unit, which makes comparison awkward. This converter translates between them using standard definitions, so you can see, for example, how the kilocalories on a nutrition label relate to kilojoules, or how a device rating in watt-hours compares to kilowatt-hours on your bill. Choose your from and to units, type a number, and the answer updates live as you type. All calculations happen locally in your browser, keeping the tool fast and private and letting it work offline once the page has loaded.