Common converters
Energy Converter
Convert joules, calories, kilowatt-hours, BTU and other energy units.
Result
3.6 MJ
1 kWh = 3.6 MJ
All units for this value
| Unit | Symbol | Value |
|---|---|---|
| Joule | J | 3600000 |
| Kilojoule | kJ | 3600 |
| Megajoule | MJ | 3.6 |
| Gigajoule | GJ | 0.0036 |
| Calorie (thermochemical, cal) | cal | 860421 |
| Kilocalorie (food Calorie) | kcal | 860.421 |
| Watt-hour | Wh | 1000 |
| Kilowatt-hour | kWh | 1 |
| Megawatt-hour | MWh | 0.001 |
| British thermal unit (IT) | BTU | 3412.14 |
| Therm (US) | thm | 0.0341296 |
| Foot-pound force | ft·lbf | 2655220 |
| Erg | erg | 3.60000e+13 |
| Electronvolt | eV | 2.24694e+25 |
| Tonne of TNT | tTNT | 0.000860421 |
About this calculator
This tool converts energy values between joules, kilojoules, megajoules, calories, kilocalories, watt-hours, kilowatt-hours, BTU, therms, foot-pounds, and electronvolts. Select your starting unit and target unit, enter a value, and the converted amount appears instantly.
How it works in plain English
Energy shows up in many everyday contexts described with different units: food labels use calories, electricity bills use kilowatt-hours, heating appliances often use BTU, and physics problems frequently use joules or electronvolts. All of these measure the same underlying quantity, work or heat, so they convert to one another through fixed numeric factors anchored to the joule, the SI unit of energy.
To convert, choose the unit your number is currently in as the "from" selection, choose the unit you want as the "to" selection, and type your value into the input box. The result recalculates live as you type, so there's no need to press a separate button. A swap control flips the "from" and "to" units instantly if you realize you picked them backwards, and an all-units table beneath the main result lists your entered value already converted into every other supported energy unit, so you can scan several equivalents at once instead of running separate conversions. You can also change the number of decimal places shown, which matters for units like electronvolts where meaningful values can be extremely small.
The formula
- 1 cal = 4.184 J
- 1 kcal = 4,184 J
- 1 kWh = 3,600,000 J
- 1 BTU (IT) = 1,055.05585262 J
- 1 ft·lbf = 1.35581794833 J
- 1 eV = 1.602176634 × 10⁻¹⁹ J
Worked example
Imagine an appliance label states it uses 0.5 kWh per cycle, and you want to know how many kilojoules that represents for a physics comparison. One kilowatt-hour equals 3,600,000 joules, so 0.5 kWh equals 1,800,000 joules, which is 1,800 kilojoules.
In the converter, you would set "from" to kilowatt-hours and "to" to kilojoules, then type 0.5. The live result shows 1,800 kJ right away. The all-units table also shows the same energy amount expressed as roughly 430.4 kcal and about 1,706.3 BTU, letting you compare the same quantity across food-energy, engineering, and everyday units without redoing the math for each one.
Energy unit equivalents relative to the joule
| Unit | Symbol | In joules (J) |
|---|---|---|
| Joule | J | 1 |
| Kilojoule | kJ | 1,000 |
| Megajoule | MJ | 1,000,000 |
| Calorie | cal | 4.184 |
| Kilocalorie | kcal | 4,184 |
| Watt-hour | Wh | 3,600 |
| Kilowatt-hour | kWh | 3,600,000 |
| British thermal unit | BTU | 1,055.05585262 |
| Therm | therm | 105,505,585.262 |
| Foot-pound force | ft·lbf | 1.35581794833 |
| Electronvolt | eV | 1.602176634 × 10⁻¹⁹ |
Values are the standard internationally defined equivalents.
Frequently asked questions
What is the difference between a calorie and a kilocalorie?
One kilocalorie equals exactly 1,000 small calories. Food energy labels almost always mean kilocalories even when they print the word "calories," which can cause confusion, since a food listing "200 calories" is really giving 200 kilocalories, not 200 of the smaller scientific calorie unit. This converter treats "calorie" and "kilocalorie" as their own distinct, clearly labeled units.
Why does my electricity bill use kilowatt-hours instead of joules?
A kilowatt-hour represents the energy used by a one-kilowatt device running for one hour, which happens to be a convenient, human-scale amount for household electricity use. A joule is far smaller in comparison, so expressing typical monthly electricity consumption in joules would involve very large, unwieldy numbers, making kilowatt-hours the more practical everyday unit.
What is a therm and where is it used?
A therm is a larger energy unit, roughly equal to 100,000 BTU, commonly used for measuring natural gas consumption on utility bills in some countries. It's a convenient scale for gas usage because household consumption often falls in a reasonable range of therms per billing period rather than requiring extremely large or small numbers.
Why is the electronvolt so much smaller than a joule?
The electronvolt is designed for describing energy at the scale of individual atoms and subatomic particles, where even a single joule would be an enormous, impractical amount. One electronvolt equals about 1.6 × 10⁻¹⁹ joules, so it takes an extremely large number of electronvolts to add up to everyday energy amounts, but it keeps particle physics numbers manageable.
Can I convert food energy labels directly with this tool?
Yes, you can enter a food label's calorie value using the kilocalorie unit, since that's what most nutrition labels actually mean by "calories," and convert it into joules, kilojoules, or any other supported energy unit. Some countries display food energy in kilojoules directly, so this tool can help translate between the two labeling conventions.
Related converters
Convert between metric, US customary and imperial length units.
Convert grams, kilograms, pounds, ounces, tons and other mass units.
Convert litres, millilitres, gallons, cups, cubic feet and more.
Convert Celsius, Fahrenheit, Kelvin and Rankine temperatures.