Energy Converter

Convert between joules, kilojoules, calories, kilocalories, watt-hours, kilowatt-hours, BTUs, electronvolts, and foot-pounds.

Value

From

Common Energy Conversions

From	To	Result
1 kcal	kJ	4.184 kJ
1 kWh	MJ	3.6 MJ
1 kWh	BTU	3,412.14 BTU
1 BTU	kJ	1.05506 kJ
1 kcal	Wh	1.16222 Wh
1 kJ	kcal	0.239006 kcal
1 J	cal	0.239006 cal
1 ft·lb	J	1.35582 J

Frequently Asked Questions

A small calorie (cal) is the energy needed to raise 1 gram of water by 1°C. A kilocalorie (kcal) = 1000 cal. Food "Calories" (with capital C) are actually kilocalories. So when a food label says "200 Calories," it means 200 kcal = 836.8 kJ.

One kilowatt-hour equals 3,600,000 joules (3.6 MJ). This is because 1 kW = 1000 J/s, and 1 hour = 3600 s. The kWh is the standard unit for electrical energy consumption on utility bills worldwide.

A British Thermal Unit (BTU) is the amount of energy needed to raise 1 pound of water by 1°F. 1 BTU ≈ 1,055.06 joules. It is used in the US for heating and cooling (HVAC), furnaces, air conditioners, and water heaters. The rest of the world uses kJ or kWh.

An electronvolt (eV) is the energy gained by an electron moving through a potential difference of 1 volt. 1 eV = 1.602 × 10⁻¹⁹ joules. It is used in particle physics, atomic physics, and quantum mechanics to describe energies of subatomic particles and photons.

A joule (J) is the SI unit of energy. A small calorie (cal) is the energy to raise 1 gram of water by 1°C, equal to 4.184 joules. A food Calorie (kcal) = 1,000 cal = 4,184 joules. Joules are used in physics and engineering; calories are used in nutrition and chemistry.

A kilowatt-hour (kWh) = 3,600,000 joules = the energy used by a 1,000-watt appliance running for one hour. Electricity bills charge per kWh. A typical US home uses about 900 kWh per month. Running a 100W light bulb for 10 hours = 1 kWh. Average US electricity cost is about $0.13–0.17 per kWh.

A BTU (British Thermal Unit) = 1,055.06 joules = the energy to raise 1 pound of water by 1°F. In HVAC, air conditioner capacity is rated in BTU/hr. A "1-ton" AC unit = 12,000 BTU/hr ≈ 3.52 kW. A typical home might need 24,000–48,000 BTU/hr of cooling depending on climate and house size.

In nutrition, the "Calorie" (capital C) = 1 kilocalorie (kcal) = 1,000 small calories. Food labels list Calories (kcal). A typical adult needs 2,000–2,500 kcal per day. 1 kcal = 4,184 joules. Fat provides 9 kcal/gram, while protein and carbohydrates each provide 4 kcal/gram.

Gasoline contains about 34.2 MJ/liter (8,176 kcal/liter) — roughly 8,000 times more energy per liter than most foods by weight. Burning 1 liter of petrol releases energy equivalent to about 8,000 food Calories. The human body is about 20–25% efficient at converting food energy to mechanical work, similar to a gasoline engine.

A megawatt-hour (MWh) = 1,000 kWh, and a gigawatt-hour (GWh) = 1,000 MWh = 1,000,000 kWh. These units are used for large-scale power generation and consumption. A large coal power plant (1 GW) running for one hour produces 1 GWh. Annual energy consumption of a country is often measured in terawatt-hours (TWh = 1,000 GWh).

About This Energy Converter

This free energy converter converts between joules, kilojoules, calories, kilocalories, watt-hours, kilowatt-hours, electron volts, BTUs, and other energy units. Enter a value in any unit for instant results across all supported units.

When to use this converter

Converting food energy between kcal and kJ
Comparing electricity consumption figures in kWh
Translating physics problems between SI and imperial energy units

Standards & References

How It Works

Enter Energy

Enter any energy value. All conversions use the joule (J) as the SI base unit of energy.

Pick Units

Choose from 10 energy units spanning everyday food calories to scientific electronvolts and engineering BTUs.

Instant Result

Results are shown instantly. Use the swap button to reverse the conversion and the reference table for quick lookups.

Common Use Cases

Nutrition & Fitness

Convert food energy between kcal and kJ for reading international nutrition labels and comparing dietary energy content.

Electricity Bills

Convert between kWh and joules/MJ to understand energy consumption on utility bills and compare costs of different energy sources.

Heating & Cooling

Convert HVAC ratings between BTU and kW/kJ for comparing heating/cooling equipment specifications across US and international markets.

Renewable Energy

Convert solar panel output, battery capacity, and energy storage between Wh, kWh, and MJ for renewable energy system design.

Physics & Chemistry

Convert between joules, electronvolts, and calories for thermodynamics problems, chemical reaction energies, and quantum physics.

Fuel & Combustion

Convert fuel calorific values between BTU, kJ, and MJ for comparing energy densities of natural gas, coal, oil, and biofuels.

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