Energy Converter

Energy Converter

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Energy Converter

Use the converter above to instantly convert between any two units of energy. This converter supports joules, kilojoules, calories, kilocalories, kilowatt-hours, BTU, megajoules, and electronvolts — covering every energy conversion you are likely to need.

Whether you are converting food calories, calculating electricity costs, working with heating systems, or doing scientific calculations, this free converter gives you an instant accurate result.

How to convert energy units

The joule is the SI base unit of energy. All other energy units can be converted to and from joules using fixed multiplication factors. For example, 1 kilocalorie = 4,184 joules, and 1 kilowatt-hour = 3,600,000 joules.

An important distinction: the calorie used in food and nutrition (shown on food labels as “Calories” with a capital C) is actually a kilocalorie — 1 food Calorie = 1,000 small calories = 4,184 joules. This causes frequent confusion when converting nutrition data.

BTU (British Thermal Unit) is commonly used in the US for heating and cooling systems. 1 BTU = 1,055.06 joules ≈ 0.293 watt-hours. Air conditioner and furnace capacities are often rated in BTU per hour.

Energy conversion reference table

Unit Joules (J) Kilocalories (kcal)
1 Joule1 J0.000239 kcal
1 Kilojoule1,000 J0.239 kcal
1 Calorie (small)4.184 J0.001 kcal
1 Kilocalorie (kcal)4,184 J1 kcal
1 BTU1,055.06 J0.252 kcal
1 Watt-hour3,600 J0.860 kcal
1 Kilowatt-hour3,600,000 J860.421 kcal
1 Megajoule1,000,000 J239.006 kcal

Frequently asked questions

How many joules are in a calorie?
1 small calorie (cal) = 4.184 joules. 1 food Calorie (kcal) = 4,184 joules. The food Calories shown on nutrition labels are actually kilocalories — 1,000 times larger than the small calorie used in chemistry.
What is a kilowatt-hour?
1 kilowatt-hour (kWh) = 3,600,000 joules = 3.6 megajoules. It is the energy consumed by a 1,000-watt appliance running for exactly one hour. Your electricity bill is measured in kWh.
How do I convert BTU to kilowatt-hours?
1 BTU = 0.000293071 kWh. To convert BTU to kWh, multiply by 0.000293. So a 10,000 BTU air conditioner uses approximately 2.93 kWh per hour of operation.
How many kilojoules are in a kilocalorie?
1 kilocalorie (kcal) = 4.184 kilojoules (kJ). This conversion is commonly needed when comparing nutrition labels from different countries — some countries list food energy in kJ while others use kcal.
What is the difference between energy and power?
Energy is the total amount of work done, measured in joules or kWh. Power is the rate at which energy is used, measured in watts (joules per second). A 100-watt bulb uses 100 joules per second. Running it for 10 hours uses 1 kWh of energy.