Need to convert energy from one unit to another? Our free Energy Converter makes it quick and easy. Enter an energy value, choose the unit you are converting from and the unit you want, and get the converted result instantly. It supports common energy units such as joules, kilojoules, calories, kilocalories, watt-hours, kilowatt-hours, BTU, electronvolts, and foot-pounds. It is useful for physics, science, electricity, engineering, nutrition, appliances, and everyday calculations.
How to Use the Energy Converter
Using the Energy Converter is simple. Enter an energy value, choose the original unit, select the unit you want to convert to, and click Convert.
- Enter an energy value.
- Select the unit under From.
- Select the unit under To.
- Click Convert.
- The converted value will appear instantly.
For example, enter 1000, select Joule (J) as the From unit and Kilojoule (kJ) as the To unit.
The result will be:
1000 J = 1 kJ
You can enter whole numbers or decimal values such as 2.5, 10.75, or 0.5.
What Is Energy?
Energy is the ability to do work or cause a change. It is involved in almost everything around us, from moving objects and heating water to powering electronic devices and producing electricity.
Energy can be measured using different units depending on the field and application.
The joule (J) is the standard SI unit of energy.
Common Energy Units
The Energy Converter supports these commonly used units:
- Joule (J)
- Kilojoule (kJ)
- Megajoule (MJ)
- Calorie (cal)
- Kilocalorie (kcal)
- Watt-hour (Wh)
- Kilowatt-hour (kWh)
- British Thermal Unit (BTU)
- Electronvolt (eV)
- Foot-pound (ft·lb)
Joule
The joule (J) is the SI unit of energy.
It is widely used in physics, engineering, science, and general energy calculations.
Because joules can represent relatively small amounts of energy, larger values are often expressed in kilojoules or megajoules.
1 kJ = 1,000 J
1 MJ = 1,000,000 J
Kilojoule
A kilojoule is equal to 1,000 joules.
1 kJ = 1,000 J
Kilojoules are commonly used in science, nutrition, engineering, and energy calculations.
Food energy may also be listed in kilojoules in some countries.
Megajoule
A megajoule equals one million joules.
1 MJ = 1,000,000 J
Megajoules are useful when describing larger amounts of energy, such as fuel energy, heating, engineering systems, and industrial applications.
Calories
A calorie is a unit of energy.
In scientific contexts, one calorie is defined as:
1 cal = 4.184 J
Calories are often associated with food and nutrition, although the calorie used on food labels is normally the kilocalorie (kcal).
Kilocalorie
A kilocalorie is equal to 1,000 calories.
1 kcal = 1,000 cal
Using the standard conversion:
1 kcal = 4,184 J
Food energy is commonly expressed in kilocalories, often simply called "Calories" with a capital C on nutrition labels.
Watt-hour
A watt-hour (Wh) is a unit of energy commonly used for electrical energy.
1 Wh = 3,600 J
It describes the amount of energy used or produced when one watt of power is maintained for one hour.
Kilowatt-hour
The kilowatt-hour (kWh) is one of the most familiar energy units in everyday electricity use.
1 kWh = 1,000 Wh
and:
1 kWh = 3,600,000 J
Electricity consumption on utility bills is commonly measured in kilowatt-hours.
For example, an appliance that uses 1,000 watts for one hour consumes approximately:
1 kWh
British Thermal Unit
The British Thermal Unit, or BTU, is a unit of energy commonly used for heating and cooling.
It is frequently encountered when discussing air conditioners, heaters, furnaces, and HVAC equipment.
For this converter:
1 BTU ≈ 1,055.05585 J
Electronvolt
An electronvolt (eV) is a very small unit of energy used primarily in physics and related scientific fields.
One electronvolt is defined as:
1 eV = 1.602176634 × 10⁻¹⁹ J
Because the value of one electronvolt is extremely small, it is particularly useful when working with particles, atoms, and other microscopic systems.
Foot-pound
The foot-pound (ft·lb) is a unit of energy used in some engineering and mechanical applications.
For this converter:
1 ft·lb ≈ 1.35582 J
It may also be encountered in torque-related contexts, where the terminology and meaning can depend on the application.
Common Energy Conversions
Some useful energy conversions include:
| Energy Unit | Equivalent |
|---|---|
| 1 kJ | 1,000 J |
| 1 MJ | 1,000,000 J |
| 1 cal | 4.184 J |
| 1 kcal | 4,184 J |
| 1 Wh | 3,600 J |
| 1 kWh | 3,600,000 J |
| 1 BTU | ≈ 1,055.05585 J |
| 1 eV | 1.602176634 × 10⁻¹⁹ J |
| 1 ft·lb | ≈ 1.35582 J |
Joules to Kilojoules
To convert joules to kilojoules, divide the number of joules by 1,000.
For example:
5,000 J = 5 kJ
This is useful when working with larger energy values where using joules would produce a long number.
Kilojoules to Joules
To convert kilojoules to joules, multiply the value by 1,000.
For example:
7 kJ = 7,000 J
Kilowatt-hours to Joules
One kilowatt-hour is equal to 3.6 million joules.
1 kWh = 3,600,000 J
For example:
2 kWh = 7,200,000 J
This conversion is useful when comparing electrical energy with scientific or engineering calculations that use joules.
Joules to Kilowatt-hours
To convert joules to kilowatt-hours, divide the number of joules by 3,600,000.
For example:
3,600,000 J = 1 kWh
This can be useful when comparing energy measurements with electricity consumption.
Calories and Kilocalories
Calories and kilocalories can sometimes cause confusion.
One kilocalorie contains 1,000 calories:
1 kcal = 1,000 cal
When food labels mention Calories with a capital "C", they generally refer to kilocalories.
Therefore:
1 food Calorie = 1 kcal = 4,184 J
Energy and Electricity
Electrical energy is commonly measured in watt-hours and kilowatt-hours.
For example, if an appliance has a power rating of 500 watts and operates for two hours, its energy use is:
500 W × 2 hours = 1,000 Wh
or:
1 kWh
The actual electricity consumption of an appliance can vary depending on how it is used.
Energy and Power
Energy and power are related, but they are not the same thing.
Energy describes the amount of work or energy used.
Power describes how quickly energy is transferred or used.
The relationship can be written as:
Energy = Power × Time
For example, using 1,000 watts for one hour results in 1 kilowatt-hour of energy consumption.
Energy in Nutrition
Energy is also used when discussing food and nutrition.
Food labels may list energy in kilocalories, kilojoules, or both.
For example, a food item might contain energy expressed as both:
500 kcal
and:
2,092 kJ
These values describe the same amount of energy using different units.
Energy in Physics
Energy is a fundamental concept in physics.
It can appear in different forms, including kinetic energy, potential energy, thermal energy, chemical energy, electrical energy, and more.
The joule is commonly used to measure these quantities.
For example, the kinetic energy of a moving object can be calculated using its mass and velocity.
Energy in Engineering
Engineers use energy measurements in many areas, including mechanical systems, electrical equipment, heating, cooling, transportation, and industrial processes.
Different industries may use different units, which makes unit conversion useful when comparing specifications or calculations.
Why Are There Different Energy Units?
Different fields developed or adopted different ways of expressing energy.
Scientists commonly use joules, electricity providers use kilowatt-hours, nutrition labels may use kilocalories or kilojoules, and heating and cooling equipment may use BTUs.
The actual amount of energy does not change when the unit changes. Only the way it is expressed changes.
Energy vs Power
It is important not to confuse energy with power.
Energy is measured using units such as:
- Joules
- Kilojoules
- Kilowatt-hours
- Calories
Power is measured using units such as:
- Watts
- Kilowatts
A device's power rating tells you how quickly it uses or transfers energy, while energy tells you the total amount involved.
Frequently Asked Questions
What is the SI unit of energy?
The joule (J) is the SI unit of energy.
How many joules are in one kilojoule?
1 kJ = 1,000 J.
How many joules are in one kilocalorie?
1 kcal = 4,184 J.
How many joules are in one kilowatt-hour?
1 kWh = 3,600,000 J.
Is a calorie the same as a kilocalorie?
No. One kilocalorie contains 1,000 calories.
1 kcal = 1,000 cal.
On food labels, "Calories" generally refers to kilocalories.
What is a kilowatt-hour?
A kilowatt-hour is a unit of energy commonly used to measure electricity consumption.
1 kWh = 1,000 Wh.
Can I convert kWh to joules?
Yes.
1 kWh = 3,600,000 J.
Can I enter decimal energy values?
Yes. You can enter values such as 2.5 kJ, 0.75 kWh, or 14.7 J.
What is the difference between energy and power?
Energy is the amount of energy transferred or used, while power describes the rate at which energy is transferred or used.
Does this converter support BTU?
Yes. You can convert BTU to joules, kilojoules, kilowatt-hours, calories, and the other available units.
Does this converter support electronvolts?
Yes. The converter includes electronvolts (eV), which are commonly used for very small energy values in physics.
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