Energy Unit Converter

Instantly convert energy values between Joules, Calories, kWh, eV, and BTUs.

Energy Value
Source Unit
Equivalents
J 0 Joules
kJ 0 Kilojoules
cal 0 Calories
kcal 0 Kilocalories
Wh 0 Watt-hours
kWh 0 Kilowatt-hours
eV 0 Electronvolts
BTU 0 British Thermal Units

Understanding Energy Units

Energy is defined as the capacity to do work. Because energy is studied in so many different fields, many different units have been developed over time.

  • Joules (J): The standard unit of energy in physics (the International System of Units). One joule is the energy transferred when applying a force of one newton over a distance of one meter.
  • Calories (cal & kcal): Used primarily in chemistry and nutrition. A "small calorie" (cal) is the energy needed to heat 1 gram of water by 1°C. A "food calorie" is actually a Kilocalorie (kcal), which is 1,000 small calories.
  • Kilowatt-hours (kWh): The standard unit for billing electrical energy. It represents the energy consumed by a 1,000-watt appliance running for one hour.
  • Electronvolts (eV): Used in quantum mechanics and particle physics. It represents the amount of kinetic energy gained by a single electron accelerating through a potential difference of one volt. Because it is incredibly small, macroscopic energy values converted to eV result in massive numbers (shown in scientific notation).
  • British Thermal Units (BTU): An older imperial unit still used for heating and air conditioning systems.