Energy Converter
Convert between joules, kilocalories, kilowatt-hours, BTU, electronvolts, and other energy units.
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How to use this calculator
- 1
Enter the energy value you want to convert.
- 2
Select the unit you are converting from (e.g. kilocalories).
- 3
Select the target unit (e.g. kilojoules).
- 4
The result updates instantly.
Frequently asked questions
How many kilojoules are in a kilocalorie?
One kilocalorie (food calorie, kcal) equals exactly 4.184 kilojoules. This is why nutrition labels sometimes show both "kcal" and "kJ" values.
What is the difference between a calorie and a kilocalorie?
In food labelling, "Calorie" (with a capital C) means kilocalorie (kcal) — 1,000 small calories. The small calorie (cal) is the energy needed to raise 1 gram of water by 1°C. When people talk about food calories, they always mean kcal.
How many kWh is 1 MJ?
1 megajoule = 0.27778 kWh. Conversely, 1 kWh = 3.6 MJ.
What is a BTU?
A British Thermal Unit (BTU) is the amount of energy needed to raise one pound of water by 1°F. 1 BTU = 1,055.06 joules. It is commonly used for air conditioners and heating systems in the US.
How many joules in a kWh?
One kilowatt-hour equals exactly 3,600,000 joules (3.6 MJ). This is because 1 kW = 1,000 J/s and 1 hour = 3,600 seconds.
Energy unit conversion guide
How to use the energy
Use this energy to onvert between joules, kilocalories, kilowatt-hours, btu, electronvolts, and other energy units. Enter your values above and get your result in seconds. The tool is free, works on all devices, and keeps your data private — nothing is stored or shared.
How the energy works
The energy converter uses standard formulas used in unit conversion in science, engineering, cooking, and everyday use. Enter your inputs, and the tool calculates the result instantly in your browser. No server-side processing means your data stays on your device. Results update in real time as you change inputs.
The joule: SI unit of energy
The joule (J) is the SI unit of energy, defined as the work done by a force of one newton over one metre. It is named after physicist James Prescott Joule. While joules are standard in physics, different fields use their own units: nutrition uses kilocalories, electricity uses kWh, and heating uses BTU.
Key energy conversion factors
1 kJ = 0.239 kcal | 1 kcal = 4.184 kJ | 1 kWh = 3,600 kJ = 3.6 MJ | 1 BTU = 1.055 kJ | 1 eV = 1.602 × 10⁻¹⁹ J | 1 ft·lb = 1.356 J.
Energy in context
A typical adult needs about 2,000 kcal (8,368 kJ) per day. A 100W light bulb uses 0.1 kWh per hour (360 kJ). A standard AA battery holds about 3,000 J (3 kJ). An average home in the US uses about 900 kWh of electricity per month.
Energy: how it works
Unit conversion matters across engineering, science, cooking, and everyday life. This tool applies internationally recognised conversion factors to deliver precise, instant results across all major unit systems — no manual lookup needed.
Who uses this tool?
Scientists, engineers, chefs, and international travellers use this tool daily to bridge the gap between different measurement systems. It eliminates the need to memorise conversion factors or hunt through reference tables.
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