Unit Conversion

Convert numbers between two units quickly and precisely

Energy Converter

Unit Conversion

Convert energy units: joule, kilocalories, kilowatt-hours, and BTU

Energy is stated in different units depending on the field: joule (J) as the SI unit, calorie (cal) and kilocalorie (kcal) in nutrition science, watt-hour (Wh) and kilowatt-hour (kWh) for electricity consumption, British thermal unit (BTU) in heating and cooling engineering, and electronvolt (eV) in atomic physics. The energy converter accurately converts values between all of these units.

Key conversion factors:

  • 1 kilojoule (kJ) = 1,000 joule (J)
  • 1 kilocalorie (kcal) = 4.184 kilojoule – common for nutrition labels (thermochemical definition)
  • 1 watt-hour (Wh) = 3,600 joule
  • 1 kilowatt-hour (kWh) = 3.6 megajoule (MJ) = 1,000 watt-hours – the basis of electricity billing
  • 1 British thermal unit (BTU) = 1,055 joule – common for heating and cooling capacity
  • 1 electronvolt (eV) = 1.602 * 10^-19 joule – standard unit in particle physics

Applications:

  • Nutrition: converting nutrition labels between kilocalories and kilojoules
  • Energy economics: calculating electricity costs and comparing household appliances in kilowatt-hours
  • Heating & cooling engineering: power ratings in BTU, e.g. for air conditioners
  • Physics & chemistry: bond and reaction energies in joule or electronvolt

The energy converter reliably supports nutrition comparisons, electricity cost calculations, and physics analyses. A note on the calorie: there are two slightly different definitions of the calorie – the thermochemical calorie (4.184 J, common for nutrition labels) and the IT calorie (4.1868 J, common in thermodynamics and heating engineering). Both are available here as separate units so you can use whichever fits your case. For molar reaction energy in chemistry (hartree, eV, kJ/mol), use the molar/atomic energy converter.

Frequently asked questions about converting energy

1 kilocalorie (kcal) equals 4.184 kilojoule (kJ), based on the thermochemical definition of the calorie. Nutrition labels on food packaging usually use this factor to convert between kcal and kJ.

1 electronvolt (eV) equals 1.602 * 10^-19 joule – an extremely small value, since eV is defined for energies at the atomic and subatomic scale, such as the energy of a single electron passing through a potential difference of 1 volt.

1 kilowatt-hour (kWh) equals 3.6 megajoule (MJ). This conversion matters when comparing physical energy figures (joule-based) with the kilowatt-hour commonly used on electricity bills.