Energy Unit Converter

Convert between units of energy.

Supported Units

• Joule (J): The joule is the SI unit of energy, named after English physicist James Prescott Joule. One joule equals the work done by a force of one newton moving an object one meter, or the energy used by one watt of power for one second. Food energy labels in many countries show kilojoules alongside calories. In physics, the joule unifies mechanical, thermal, and electrical energy into a single consistent unit.
• Kilojoule (kJ): The kilojoule equals 1,000 joules and is used for food energy labeling in Australia, New Zealand, and many other countries. A typical adult requires about 8,400 kJ (2,000 kcal) of food energy per day. In chemistry, enthalpy changes are commonly expressed in kJ per mole, and the heat of vaporization of water is approximately 2,257 kJ per kilogram.
• Calorie (thermochemical) (cal): The thermochemical calorie is a unit of energy originally defined as the amount needed to raise the temperature of one gram of water by one degree Celsius. It is exactly 4.184 joules. Note that the "Calorie" seen on food labels is actually a kilocalorie (1,000 calories). The calorie has deep roots in calorimetry and chemistry, and although the SI system favors joules, calories remain widely used in everyday discussions of food and diet.
• Kilocalorie (kcal): The kilocalorie equals 1,000 thermochemical calories and is the standard unit for food energy labeling in Japan, the United States, and many other countries. It is often written as "Cal" (with a capital C) or simply called a "Calorie" on food packages. A bowl of rice (150 grams) contains about 235 kcal, a slice of bread about 160 kcal, and 30 minutes of walking burns roughly 100 kcal.
• Watt-hour (Wh): The watt-hour is a unit of energy equal to 3,600 joules, representing the energy used by one watt of power over one hour. It is commonly used for portable battery capacities; a typical power bank rated at 5,000 mAh at 3.7 V holds about 18.5 Wh. Airline regulations for lithium-ion batteries are also specified in watt-hours, with batteries under 100 Wh generally permitted in carry-on luggage.
• Kilowatt-hour (kWh): The kilowatt-hour equals 1,000 watt-hours and is the standard billing unit for household electricity. An average Japanese household uses about 300 kWh per month, and electricity costs roughly 25 to 40 yen per kWh. Electric vehicle batteries range from about 40 to 100 kWh, providing approximately 6 to 8 km of range per kWh. Solar panel output is also measured in kWh.
• Electronvolt (eV): The electronvolt is a unit of energy widely used in particle physics and quantum mechanics. It equals the energy gained by a single electron accelerating through a potential difference of one volt, approximately 1.602 times 10 to the minus 19 joules. Visible light photons have energies of about 1.8 to 3.1 eV, X-rays range from a few keV to hundreds of keV, and particle accelerators work with energies of GeV to TeV. Semiconductor band gaps are also expressed in eV, with silicon at about 1.12 eV.
• British thermal unit (BTU): The British thermal unit is the amount of energy needed to raise the temperature of one pound of water by one degree Fahrenheit. It is primarily used in the American HVAC industry, where air conditioner capacity is rated in BTU per hour (12,000 BTU/h equals one ton of refrigeration). Residential air conditioners typically range from 5,000 to 25,000 BTU/h. Natural gas is also traded in BTU, with one cubic foot containing about 1,000 BTU. One BTU equals approximately 1,055 joules.

How to Use

1. Select the unit you want to convert from in the "From" dropdown.

2. Select the unit you want to convert to in the "To" dropdown.

3. Enter a value and the result will be displayed in real time.

4. Use the swap button to reverse the conversion direction.