Energy Converter
Convert between joules, calories, kilowatt-hours and other energy units.
The Energy Converter is a free online tool that converts between joules, calories, kilowatt-hours (kWh), and British thermal units (BTU) instantly. No sign-up needed — enter a value, choose your units, and get an accurate result. It's a useful reference when comparing appliance energy labels, reading nutrition information, or working through physics homework.
What is an energy converter?
Energy is measured differently depending on the field: physics uses joules, nutrition uses calories, electricity bills use kilowatt-hours, and heating and cooling systems use BTUs. This tool lets you move between them without memorizing conversion factors, useful for schoolwork, engineering, or comparing energy bills and appliances. Because these units serve very different purposes, converting between them accurately requires precise, standardized conversion factors rather than rough estimates.
How to use the Energy Converter
- Enter the energy value you want to convert.
- Select the unit to convert from — joules, calories, kWh, or BTU.
- Click Calculate to see the equivalent across units.
Key features
- Supports joules, kilojoules, calories, kilocalories, kWh and BTU.
- Useful for physics, nutrition, and energy bill comparisons.
- Instant, accurate two-way conversion.
- Free and works directly in your browser.
Related tools
Working with related units too? Try the Power Converter, Torque Converter, or the Pressure Converter.
Frequently asked questions
Is the Energy Converter free?
Yes, completely free with no sign-up or usage limits. There's no limit on how many conversions you can perform, and no account is required.
How many joules are in a calorie?
One calorie equals approximately 4.184 joules. This is why nutrition labels sometimes list values in both calories and kilojoules.
What is a kilowatt-hour?
A kilowatt-hour is the energy used by a 1,000-watt appliance running for one hour — it's the standard unit used on electricity bills. Your monthly electricity bill is essentially a running total of kilowatt-hours consumed over the billing period.
Why do heating systems use BTUs?
The British thermal unit historically measures the heat needed to raise one pound of water by one degree Fahrenheit, and it remains common in HVAC and appliance ratings. Many air conditioner and furnace ratings still list BTU output alongside or instead of watts.
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