Available Energy units

• joule conversions

  The joule is the SI base unit of energy. It is the standard unit for work, heat, and electrical energy in physics, engineering, and scientific measurement worldwide.

• kilojoule conversions

  A kilojoule is a unit of energy equal to 1,000 joules. It is commonly used in nutrition to express the energy content of food, as well as in thermodynamics and mechanical engineering.

• kilowatt hour conversions

  A kilowatt hour is a unit of energy equal to 1,000 watt hours. It is the standard billing unit used by electricity providers worldwide to measure household and commercial energy consumption.

• calorie (thermochemical) conversions

  The thermochemical calorie is a unit of energy equal to approximately 4.184 joules. It is used in chemistry and physics to express small heat quantities, particularly in thermochemical experiments.

• kilocalorie (dietary) conversions

  A kilocalorie, written as Calorie with a capital C in nutrition contexts, is a unit of energy equal to 1,000 thermochemical calories. It is the standard unit used to express the energy content of food on nutrition labels globally.

• watt hour conversions

  A watt hour is a unit of energy equal to the power of one watt sustained for one hour. It is used to measure small amounts of electrical energy consumption, particularly in battery capacities and portable electronics.

• megajoule conversions

  A megajoule is a unit of energy equal to one million joules. It is used in industrial energy calculations, explosive yield estimations, and large-scale thermodynamic systems.

• electronvolt conversions

  An electronvolt is a unit of energy equal to the work done on an electron by a potential difference of one volt, approximately 1.602 × 10⁻¹⁹ joules. It is used in atomic physics, particle physics, and quantum mechanics.

• British thermal unit conversions

  A British thermal unit (BTU) is an energy unit defined as the heat needed to raise one pound of water by one degree Fahrenheit. It is used in HVAC systems, heating and cooling equipment ratings, and natural gas billing in the United States.

• therm (US) conversions

  A US therm is a unit of energy equal to 100,000 BTU. It is used by gas utility companies in the United States as the standard billing unit for natural gas consumption.

Assumption: calorie means thermochemical calorie, and therm means US therm.

Full Energy conversion matrix

About Energy

Units of energy and work

Real-world uses

Energy units appear in electricity bills (kilowatt-hours), food labels (kilocalories or kilojoules), fuel specifications (British thermal units), and scientific research (electronvolts). Power utilities bill residential customers per kWh consumed. Nutritionists quantify dietary intake in Calories (kcal), while physicists measure particle interactions in electronvolts. Natural gas is traded in therms or gigajoules, and building energy performance certificates rate consumption in kWh per square metre per year.

History

James Prescott Joule established the mechanical equivalent of heat in the 1840s, proving that work and heat are interconvertible. The calorie was defined by Nicolas Clément in 1824 as the heat needed to raise one gram of water by one degree Celsius. The British thermal unit evolved from similar calorimetric experiments in the Imperial system. The joule became the SI unit of energy in 1960, honouring Joule's foundational experiments.

Common mistakes

The most common confusion is between calories and Calories (kilocalories): food labels list "Calories" with a capital C, each equalling 1,000 scientific calories. People also mix up kilowatt-hours (energy) with kilowatts (power), mistakenly treating them as interchangeable. Another error is equating BTU values across fuel types without accounting for combustion efficiency.

Measurement standards

The joule is the SI derived unit of energy, defined as one kilogram-metre-squared per second-squared (kg·m²/s²). The kilowatt-hour, equal to exactly 3.6 megajoules, is accepted for use with the SI by the BIPM for practical electricity metering.

Did you know?

A single bolt of lightning releases roughly 1 to 5 gigajoules of energy, yet only a small fraction reaches the ground as electrical current. Most of the energy dissipates as light, heat, and the thunder shockwave.

Common values