Energy Converter

Reviewed by the CalculatorHub team, edited by James Graham. NIST-defined conversion factors. Last verified 14 June 2026.

Energy is the capacity to do work, and it can be measured in many different units depending on context and history. The SI unit is the joule (J), equal to one newton-metre of work, but a joule is small: an AA battery stores about 10,000 joules. Larger quantities use kilojoules (kJ), megajoules (MJ), and gigajoules (GJ). In electricity, the kilowatt-hour (kWh) is universal: it represents the energy consumed by a 1,000-watt appliance running for one hour, and equals 3.6 million joules. This is how electricity companies meter and bill consumption. The calorie (cal), originally defined in chemistry as the energy to raise 1 gram of water by 1 degree Celsius, equals 4.184 joules. Confusingly, the unit used in food and nutrition ('Calories' with a capital C) is actually a kilocalorie (4,184 joules), about 1,000 times larger. The BTU (British Thermal Unit), used in HVAC systems and building engineering in the United States, equals about 1,055 joules. Mechanical engineers use foot-pounds (ft.lbf), and particle physicists use electronvolts (eV) for subatomic particles. Converting between these units is essential when comparing electricity bills, understanding food nutrition, evaluating heating and cooling systems, or reading physics literature. This calculator displays twelve energy units: joules through electronvolts. Enter a value in any field and all others update instantly.