Convert energy between joules, kilojoules, kilowatt-hours, calories, BTU, and electronvolts. Food Calories and small calories are labeled separately, and the two BTU conventions remain distinct.
How to use this calculator
Select the unit from your bill, label, or calculation, then choose the destination. To convert kilojoules to food Calories, choose kJ and Food Calories / kilocalories. Reverse those selections to convert nutrition Calories to kJ. The equivalent table helps compare several units without repeating the input.
Food Calories, electricity, and heat
A food Calorie is a kilocalorie: 1,000 small calories. This calculator uses the thermochemical definition, giving 1 kcal = 4.184 kJ. It converts a stated energy quantity; it does not estimate food composition or personal calorie needs.
A kilowatt-hour measures energy, while a kilowatt measures power. A device drawing 1 kW steadily for one hour uses 1 kWh. Converting an electricity bill to joules does not require a tariff, but calculating cost does.
BTU values depend on the definition. International Table and thermochemical options are separate. If a technical document specifies one, use that option instead of treating the two as identical.
Examples
A food label
836.8 kJ = 200 kcal, or 200 food Calories. Choosing small calories instead would show 200,000 cal.
A household electricity quantity
2.5 kWh = 9 MJ = 9,000 kJ. The conversion is independent of how much the electricity provider charges per kWh.
Formula
target energy = source energy × source factor / target factor
1 kWh = 3,600,000 J = 3,600 kJ
1 kcal (thermochemical) = 4,184 J
food Calories = kilojoules / 4.184
Precision and interpretation
Negative energy changes can be converted with their sign preserved. The tool does not equate torque with energy merely because both can involve newton meters. Displayed values are rounded to the selected significant digits; very small electronvolt conversions use scientific notation.
Definitions and further reading
Unit and quantity reference provides the underlying definitions. The examples above are worked calculations for this tool.