Converters
Energy Converter
Convert J, kJ, MJ, Wh, kWh, cal, kcal, and BTU.
Energy Converter tool
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About This Tool
Convert energy measurements used in electricity, physics, heating, engineering, and technical specifications from one unit to another. Enter a value once and compare joules, kilojoules, megajoules, watt-hours, kilowatt-hours, thermochemical calories, kilocalories, and British thermal units. All calculations run locally in your browser.
How To Use It
- Enter the energy value you want to convert.
- Choose its current unit, such as kWh, J, or BTU.
- Choose the destination unit and read the converted result.
- Use the comparison table to see the same energy amount in every supported unit.
Examples
1 kWh to MJ
One kilowatt-hour equals exactly 3.6 megajoules because 1 watt is 1 joule per second and one hour contains 3,600 seconds.
1 Wh to joules
One watt-hour equals exactly 3,600 joules.
1 kcal to joules
Using the thermochemical calorie, 1 kilocalorie equals 4,184 joules.
Useful Notes
Joule is the SI energy unit
The joule (J) is the SI derived unit of energy. Kilojoules and megajoules are 1,000 and 1,000,000 joules respectively, making them convenient for larger quantities.
Watt-hours measure energy, not power
A watt is a rate of energy transfer, while a watt-hour is energy accumulated over time. One Wh equals 3,600 J, so one kWh equals 3,600,000 J or 3.6 MJ.
This tool uses the thermochemical calorie
The word calorie can refer to slightly different historical definitions. This converter uses the thermochemical calorie, defined as exactly 4.184 J. One kilocalorie is therefore 4,184 J. Food labels commonly use Calories with a capital C to mean kilocalories, but nutrition interpretation is outside this unit converter's scope.
BTU definition used
British thermal unit definitions vary slightly by convention. This converter uses the International Table BTU value of 1,055.05585262 J per BTU and states that convention so results can be reproduced.
Negative values represent signed energy changes
The converter accepts negative numbers because some calculations use signed changes in energy. The sign is preserved during unit conversion; the tool does not decide the physical meaning of that sign for a particular system.
FAQ
How many joules are in 1 kWh?
One kilowatt-hour equals exactly 3,600,000 joules.
Is kWh a unit of power?
No. Kilowatt-hour is a unit of energy. Kilowatt is a unit of power, which describes the rate at which energy is transferred or used.
Which calorie does this converter use?
It uses the thermochemical calorie: exactly 4.184 joules per calorie and 4,184 joules per kilocalorie.
Why can BTU conversions differ slightly elsewhere?
Several BTU conventions exist. This tool uses the International Table BTU value of 1,055.05585262 joules per BTU, so a source using another convention may differ slightly.