Energy Converter
Convert energy measurements between common units using this free online calculator.
Conversion Result
Results are calculated using the conversion factors listed below and may be rounded for display.
About This Energy Converter
Energy is the capacity to do work or produce change. Different fields use different units to describe it. Scientists commonly use joules, electrical bills use kilowatt-hours, and food labels commonly use kilocalories or Calories. This converter helps you compare these measurements without performing the calculations manually.
Choose the starting unit, select the unit you want, enter your value, and select Convert Energy. The result appears below the form. You can also convert zero and negative numerical values when they are appropriate for a difference or signed calculation.
Common Energy Units
Joule (J): The standard SI unit of energy.
Kilojoule (kJ): Equal to 1,000 joules.
Megajoule (MJ): Equal to 1,000,000 joules.
Calorie (cal): A small calorie, defined here as 4.184 joules.
Kilocalorie (kcal): Equal to 1,000 small calories. On many food labels, one dietary Calorie (Cal) means one kilocalorie.
Watt-hour (Wh): Equal to 3,600 joules and used to express electrical energy.
Kilowatt-hour (kWh): Equal to 3.6 million joules and commonly used for electricity consumption.
British thermal unit (BTU): A unit used in heating, cooling and other energy applications. This calculator uses the international-table BTU approximation.
Foot-pound (ft·lb): A unit used to measure work or energy.
Erg: A small energy unit used in the centimetre-gram-second system.
US therm (thm): A large energy unit commonly associated with natural gas measurement.
Energy Conversion Formula
Each factor represents the approximate number of joules in one unit. This lets the calculator convert between any two supported units.
Useful Energy Conversion Values
- 1 kJ = 1,000 J
- 1 MJ = 1,000,000 J
- 1 Wh = 3,600 J
- 1 kWh = 3,600,000 J
- 1 kcal = 4,184 J
- 1 cal = 4.184 J
- 1 MWh = 1,000 kWh
Conversion factors depend on the unit definition. For example, this page uses the international-table BTU and the US therm. Other definitions may differ slightly.
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Frequently Asked Questions
What is the SI unit of energy?
The joule (J) is the International System of Units (SI) unit of energy.
How many joules are in one kilojoule?
One kilojoule is equal to 1,000 joules.
How many joules are in one kilowatt-hour?
One kilowatt-hour equals 3,600,000 joules.
How do I convert calories to kilojoules?
Select calorie (cal) as the source unit and kilojoule (kJ) as the target unit, enter your value, and click Convert Energy. One small calorie is approximately 0.004184 kJ.
What is the difference between cal and kcal?
One kilocalorie (kcal) equals 1,000 small calories (cal). Food labels often use the word Calories for kilocalories.
Can I convert electricity usage into joules?
Yes. Select kWh as the source unit and J as the target unit. Multiply the number of kilowatt-hours by 3,600,000 to obtain joules.
Is this energy converter free?
Yes. You can use this online calculator without paying a fee or installing software.