Energy Converter
Convert between joules, kilocalories, kilowatt-hours, BTU, electronvolts, and other energy units.
Did this tool work for you?
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
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.
Learn more from an authoritative source:
NISTPower Converter
Convert between watts, kilowatts, horsepower, BTU/hour, and other power units.
Number Base Converter
Convert numbers between decimal, binary, hexadecimal, and octal instantly.
Force Converter
Convert between newtons, kilonewtons, pound-force, kilogram-force, dynes, and more.
Angle Converter
Convert between degrees, radians, gradians, arcminutes, arcseconds, and revolutions.
Fuel Consumption Converter
Convert between MPG (US), MPG (UK), L/100km, and km/L fuel efficiency units.
Frequency Converter
Convert between hertz, kilohertz, megahertz, gigahertz, and RPM.
Results are estimates for informational purposes only and do not constitute professional financial, medical, legal, or technical advice. Read full disclaimer →