Free Energy Converter - Joules, Calories, kWh, BTU

Convert between energy units: joules, kilojoules, calories, kilocalories, watt-hours, kilowatt-hours, BTU and electronvolts.

What Is Energy Converter?

Energy is measured in different units across different fields — joules in physics, calories in nutrition, kilowatt-hours on electricity bills, BTU in heating systems and electronvolts in particle physics. Converting between these units is necessary when working across disciplines or comparing energy quantities from different sources.

One kilowatt-hour (the unit on your electricity bill) equals 3,600,000 joules. A dietary calorie (kcal) equals 4,184 joules. These relationships are fixed physical constants, so the conversion is always exact. This tool handles all common energy units and the less common ones used in specialised fields.

How to Use This Tool

  1. Enter the energy value you want to convert.
  2. Select the source unit (joules, calories, kWh, BTU, etc.).
  3. Select the target unit.
  4. View the converted result instantly.

Tips & Best Practices

  • A dietary "calorie" (Calorie with a capital C) is actually a kilocalorie (1,000 small calories) — this is a common source of confusion.
  • One kWh on your electricity bill is the energy used by a 1,000-watt appliance running for one hour.
  • BTU (British Thermal Units) are used in the US and UK for heating and air conditioning capacity.
  • Joules are the SI standard — when in doubt, convert to joules as a common baseline.

Common Use Cases

  • Converting between energy units for physics or engineering calculations.
  • Comparing energy values across different measurement systems.
  • Understanding nutritional energy (calories) in relation to physical energy units.
  • Converting heating or cooling capacity specifications between BTU and kW.

Frequently Asked Questions

How many joules in a calorie?

1 food Calorie (kcal) = 4,184 Joules. A small calorie (cal) = 4.184 Joules.