Precision Utility
Energy
Converter
Supported
7 Units
Results
Instant Convert
Convert between common energy units in real time. Enter a value, choose your source and target units, and see the result instantly. Supports joules, kilojoules, calories, kilocalories, watt-hours, kilowatt-hours and BTU.
Conversion Input
Converted Value
239.006
Kilocalories (kcal)
Input
1,000
From
kJ
To
kcal
Factor
0.2390
How the energy converter works
Enter the energy value you want to convert, then pick a source unit and a target unit from the dropdown menus. The result updates automatically as you type or change units.
Internally, every conversion passes through joules as the base unit. Your input is first converted to joules, then from joules to the target unit. This two-step approach keeps the maths clean and ensures every unit pair is covered.
The conversion factors used are standard SI definitions. One kilojoule is 1,000 joules, one calorie is 4.184 joules, one watt-hour is 3,600 joules, and one BTU is approximately 1,055.06 joules.
Use the swap button between the unit selectors to quickly reverse the conversion direction without re-entering your value.
What you need to know about energy units
Energy is measured in many different units depending on the field. Physics and engineering typically use joules and kilowatt-hours, while nutrition uses kilocalories and food labelling often just says "Calories" (capital C) to mean kcal.
Key facts:
- The joule (J) is the SI unit of energy, defined as the work done by a force of one newton over one metre
- One kilocalorie (kcal) = 4,184 joules — this is the "Calorie" you see on food packaging
- One kilowatt-hour (kWh) = 3,600,000 joules — the unit your electricity bill is measured in
- One BTU = 1,055.06 joules — commonly used in heating and air-conditioning specifications
- Watt-hours and kilowatt-hours measure energy consumed over time, which is why they appear on utility bills
Understanding these relationships helps you compare energy values across different contexts — from food labels to electricity bills to scientific calculations.
Frequently asked questions
How do I convert joules to kilowatt-hours?
Divide the number of joules by 3,600,000. One kilowatt-hour equals 3.6 million joules. For example, 7,200,000 J = 2 kWh.
What is the difference between a calorie and a kilocalorie?
One kilocalorie (kcal) equals 1,000 calories (cal). The "Calories" shown on food labels are actually kilocalories. One kcal is the energy needed to raise 1 kg of water by 1 degree Celsius.
How many joules are in one BTU?
One British Thermal Unit (BTU) equals approximately 1,055.06 joules. BTU is commonly used in heating and cooling systems to measure thermal energy.
Why is the joule the SI unit of energy?
The joule is the SI unit of energy because it provides a consistent, universal measure. One joule equals the work done when a force of one newton moves an object one metre. It is named after James Prescott Joule.
How do I convert calories to joules?
Multiply the number of calories by 4.184. One thermochemical calorie equals exactly 4.184 joules. For example, 500 cal = 2,092 J.
What is a watt-hour and how does it relate to joules?
A watt-hour (Wh) is the energy consumed by one watt of power over one hour. One watt-hour equals 3,600 joules. Kilowatt-hours (kWh) are the standard billing unit for electricity in the UK.