Power Converter
Convert power between watts, kW, hp and BTU/h.
Unit Converters
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Energy Converter
Joules, kWh, calories and BTU in one place.
Energy Converter tool
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Result
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To twelve digits
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Conversion factor
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The other way
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In scientific notation
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About the Energy Converter
Energy Converter brings together units from physics, nutrition, electricity and heating, which all measure the same quantity in mutually incomprehensible scales. Joules for physics, calories for food, kilowatt hours for electricity, BTU and therms for gas and heating.
The food calorie is the one that causes confusion. A 'calorie' on a nutrition label is really a kilocalorie: 4,184 joules, not 4.184. A 2,000-calorie diet is 8.4 megajoules, which is why labels in some countries state kilojoules instead. Both appear here, as separate units, with the thousand-fold difference between them explicit.
The useful conversion to remember is that a kilowatt hour is exactly 3.6 megajoules, since a watt is a joule per second and an hour is 3,600 seconds. It is also why the electricity calculator and the heating calculator can be compared at all: once everything is in joules, a unit of gas and a unit of electricity hold the same energy.
The page shows its working, not just its answer. Where there is a formula it is printed with your own numbers substituted in, so you can check the result rather than take it on trust -- which is the difference between a calculator you can use for something that matters and one you cannot.
Everything runs inside your browser. What you type is never uploaded, never logged and never stored, and the calculator keeps working if your connection drops after the page has loaded.
Looking for something this does not cover? FreeToolsHub.org is another hub of free online tools that need no account, and it is worth a look if energy converter is only part of what you are working on.
How to use the Energy Converter
- Choose from and toThe fields below change to match what you pick, so only the figures that matter to your case are asked for.
- Enter valueDecimals are fine, and thousands separators are accepted and ignored.
- Read the result, to twelve digits and conversion factorThe figures update as you type. The Calculate button is there if you would rather press something, but nothing waits for it.
- Copy or check the resultCopy the summary with the copy button, or open the table to check it row by row.
Features
- Shows result, to twelve digits, conversion factor, the other way and in scientific notation together, so you are not running it twice
- A results table you can read across
- Updates as you type, with no button to press and no page reload
- Copy the result in one click
- Free, no sign-up, and it runs entirely in your browser
Who uses this tool
The energy converter is used by writers, developers, students, marketers and anyone else who needs the job done once without installing software. Common cases include:
- Converting a food label between calories and kilojoules
- Comparing a gas bill in therms with electricity in kWh
- Converting an appliance rating from BTU to watts
- Getting joules for a physics calculation
Frequently asked questions
Is a food calorie the same as a calorie?
No. A food calorie is a kilocalorie, a thousand small calories. The label says Calories with a capital C in some conventions, which does not help.
How many joules in a kilowatt hour?
Exactly 3,600,000, or 3.6 megajoules, because a watt is a joule per second and an hour is 3,600 seconds.
What is a therm?
About 105.5 megajoules, or 100,000 BTU. It is the unit gas is usually billed in, which is why comparing a gas bill with an electricity bill needs a conversion.
Related tools
If the energy converter is not quite what you need, these other free tools solve closely related problems, and there are 18 more in unit converters.
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Checked and rebuilt on 2026-10-14. The method this calculator uses is described in the section above, and corrections go through the contact page.