Energy Converter
Convert between energy units instantly
| Kilocalorie (kcal) | Kilojoule (kJ) |
|---|---|
| 0.1 | 0.4184 |
| 1 | 4.184 |
| 5 | 20.92 |
| 10 | 41.84 |
| 50 | 209.2 |
| 100 | 418.4 |
How to use
Enter a value and select the source and target energy units. The converter supports 11 units across four systems: Metric (joule, kilojoule, megajoule), Electrical (watt-hour, kilowatt-hour, electronvolt), Thermal (calorie, kilocalorie, BTU, therm), and Mechanical (foot-pound). Results update instantly as you type or change units. Use the swap button to quickly reverse the conversion direction.
Examples
Food calories to kilojoules
A food label shows 250 kcal per serving. Convert to kilojoules: 250 kcal = 1,046 kJ. Food energy in most countries outside the US is labeled in kilojoules. One kilocalorie (food Calorie) equals 4.184 kJ.
Electricity consumption in kWh
A space heater uses 5,400,000 joules over 1.5 hours. Convert to kilowatt-hours: 5,400,000 J = 1.5 kWh. Electric bills are measured in kilowatt-hours, where 1 kWh = 3,600,000 joules.
Heating energy in BTU
A furnace is rated at 80,000 BTU/hour. Convert to kilowatt-hours: 80,000 BTU = 23.45 kWh. BTU (British Thermal Units) are commonly used for heating and cooling capacity ratings in the US.
Frequently asked questions
What is the difference between calories and kilocalories?
A calorie (cal) is the energy needed to raise 1 gram of water by 1 degree Celsius. A kilocalorie (kcal) equals 1,000 calories. The "Calories" on food labels are actually kilocalories. When a food label says 200 Calories, it means 200 kcal or 200,000 cal. One kilocalorie equals 4.184 kilojoules.
What is the difference between joules and calories?
Both are units of energy. The joule (J) is the SI unit of energy, defined as the work done by a force of one newton over one meter. The calorie is an older unit based on heating water. One calorie equals 4.184 joules. Joules are used in physics and engineering, while calories are common in nutrition and chemistry.
What is a kilowatt-hour?
A kilowatt-hour (kWh) is the energy consumed by a 1,000-watt appliance running for one hour. It equals 3,600,000 joules or 3,600 kilojoules. Electric utility companies bill in kWh. For example, a 100-watt light bulb running for 10 hours uses 1 kWh of energy.
What is a BTU?
A BTU (British Thermal Unit) is the amount of heat needed to raise the temperature of one pound of water by one degree Fahrenheit. One BTU equals approximately 1,055 joules. BTUs are commonly used in the US for rating heating and cooling equipment, natural gas billing, and air conditioning capacity.
What is an electronvolt used for?
An electronvolt (eV) is the energy gained by a single electron moving through an electric potential of one volt. It equals 1.602 x 10^-19 joules, an extremely small amount of energy. Electronvolts are used in particle physics, quantum mechanics, and semiconductor physics where energies at the atomic scale are measured.
About this tool
Convert between energy units including joules, calories, kilowatt-hours, BTU, electronvolts, and more. Instant results with quick reference table.
All calculations are performed locally in your browser. Your data never leaves your device.