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Use the overview below to better understand the meaning and history of the different weight units.

Q unit (1,055,055,900,000,000,000,000 J)
Unit of energy equal to one quintillion (10¹⁸) Btu, 1000 quads, or 293,000 terawatt hours (TWh).

Quad (1,055,055,900,000,000,000 J)
A quad is a unit of energy equal to 1015 (a shortscale quadrillion) BTU, or 1.055 × 1018 joules (1.055 exajoules or EJ) in SI units. The unit is used by the U.S. Department of Energy in discussing world and national energy budgets. The global primary energy production in 2004 was 446 quad, equivalent to 471 EJ.

Exajoule (1,000,000,000,000,000,000 J)
The exajoule (EJ) is equal to one quintillion (10¹⁸) joules. The 2011 Tōhoku earthquake and tsunami in Japan had 1.41 EJ of energy according to its rating of 9.0 on the moment magnitude scale. Yearly U.S. energy consumption amounts to roughly 94 EJ.

Terawatthour (3,600,000,000,000,000 J)
The terawatthour hour (symbol TWh) is a unit of energy equal to 3,600 terajoules. If energy is transmitted or used at a constant rate (power) over a period of time, the total energy in terawatt hours is equal to the power in terawatts multiplied by the time in hours.

Petajoule (1,000,000,000,000,000 J)
The petajoule (PJ) is equal to one quadrillion (1015) joules. 210 PJ is about 50 megatons of TNT. This is the amount of energy released by the Tsar Bomba, the largest manmade explosion ever.

Gigawatt hour (3,600,000,000,000 J)
The gigawatt hour (symbol GWh) is a unit of energy equal to 3,600,000 megajoules. If energy is transmitted or used at a constant rate (power) over a period of time, the total energy in gigawatt hours is equal to the power in gigawatt multiplied by the time in hours.

Terajoule (1,000,000,000,000 J)
The terajoule (TJ) is equal to one trillion (10¹²) joules; or about 0.278 GWh (which is often used in energy tables). About 63 TJ of energy was released by the atomic bomb that exploded over Hiroshima. The International Space Station, with a mass of approximately 450 megagrams and orbital velocity of 7.7 km/s, has a kinetic energy of roughly 13 TJ. In 2017 Hurricane Irma was estimated to have a peak wind energy of 112 TJ.

Tonnes of oil equivalent (41,868,000,000 J)
Tonne of oil equivalent (toe) is a unit of energy, defined as the amount of energy released by burning one tonne (1000 Kilograms) of crude oil.

Tonnes of coal equivalent (29,307,600,000 J)
The ton of coal equivalent is the energy that is product of burning one metric ton (or tonne) of coal. The metric ton (or tonne) is a unit of mass equal to 1,000 kilograms or 2,204.6 pounds.

Ton (explosive) (4,184,000,000 J)
TNT equivalent is a convention for expressing energy, typically used to describe the energy released in an explosion. The "ton of TNT" is a unit of energy defined by that convention to be 4.184 gigajoules, which is the approximate energy released in the detonation of a metric ton (1,000 kilograms or one megagram) of TNT. In other words, for each gram of TNT exploded, 4,184 joules of energy are released. This convention intends to compare the destructiveness of an event with that of traditional explosive materials, of which TNT is a typical example, although other conventional explosives such as dynamite contain more energy.

Megawatthour (3,600,000,000 J)
The megawatt hour (symbol MWh) is a unit of energy equal to 3,600 megajoules. If energy is transmitted or used at a constant rate (power) over a period of time, the total energy in megawatt hours is equal to the power in megawatt multiplied by the time in hours.

Dekatherm (1,055,057,000 J)
A dekatherm (dth) is a unit of energy used primarily to measure natural gas, developed in about 1972 by the Texas Eastern Transmission Corporation, a natural gas pipeline company. It is equal to 10 therms or 1,000,000 British thermal units (MMBtu) or 1.055 GJ. It is also approximately equal to one thousand cubic feet (Mcf) of natural gas or exactly one Mcf of natural gas with a heating value of 1000 Btu/cf.

Gigajoule (1,000,000,000 J)
The joule (/dʒuːl/; symbol: J) is a derived unit of energy in the International System of Units. It is equal to the energy transferred to (or work done on) an object when a force of one newton acts on that object in the direction of its motion through a distance of one metre (1 newton metre or N⋅m). It is also the energy dissipated as heat when an electric current of one ampere passes through a resistance of one ohm for one second. It is named after the English physicist James Prescott Joule (1818–1889).

Therm (105,505,600 J)
Not to be confused with Thermies unit. The therm (symbol, thm) is a nonSI unit of heat energy equal to 100,000 British thermal units (Btu). It is approximately the energy equivalent of burning 100 cubic feet (2.83 cubic metres) – often referred to as 1 CCF – of natural gas. Since natural gas meters measure volume and not energy content, a therm factor is used by natural gas companies to convert the volume of gas used to its heat equivalent, and thus calculate the actual energy use. The therm factor is usually expressed in units of therms per CCF. It will vary with the mix of hydrocarbons in the natural gas. Natural gas with a higher than average concentration of ethane, propane or butane will have a higher therm factor. Impurities, such as carbon dioxide or nitrogen, lower the therm factor. One therm is equal to about 105.5 megajoules, 25200 kilocalories, or 29.3 kilowatthours. One therm can also be provided by about 96.7 cubic feet (2.74 m3) of natural gas. The therm sometimes has been confused with the thermie. The names of both units come from the Greek word for heat.

Thermie (4,185,800 J)
A thermie (th) is a nonSI metric unit of heat energy, part of the metretonnesecond system sometimes used by European engineers. The thermie is equal to the amount of energy required to raise the temperature of 1 tonne (1,000 kg) of water at 14.5 °C at standard atmospheric pressure by 1 °C. The thermie is equivalent to 1,000 kilocalories, 4.1868 megajoules or 3968.3 BTU.

Kilowatt hour (3,600,000 J)
The kilowatt hour (symbol kWh, kW⋅h or kW h) is a unit of energy equal to 3.6 megajoules. If energy is transmitted or used at a constant rate (power) over a period of time, the total energy in kilowatt hours is equal to the power in kilowatts multiplied by the time in hours. The kilowatt hour is commonly used as a billing unit for energy delivered to consumers by electric utilities.

Horsepower hour (2,684,519 J)
A horsepowerhour (hph or hp⋅h) is an outdated unit of energy, not used in the SI system of units. The unit represents an amount of work a horse is supposed capable of delivering during an hour (1 (one) horsepower integrated over a time interval of an hour). The horsepowerhour is still used in the railroad industry when sharing motive power (locomotives.) For example, if Railroad A borrows a 2,500 horsepower locomotive from Railroad B and operates it for twelve hours, Railroad A owes a debt of (2,500 hp × 12 h) = 30,000 hp⋅h. Railroad A may repay the debt by loaning Railroad B a 3,000 horsepower locomotive for ten hours.

Megajoule (1,000,000 J)
The megajoule (MJ) is equal to one million (106) joules, or approximately the kinetic energy of a one megagram (tonne) vehicle moving at 161 km/h. The energy required to heat 10 liters of liquid water at constant pressure from 0 °C (32 °F) to 100 °C (212 °F) is approximately 4.2 MJ. One kilowatt hour of electricity is 3.6 megajoules.

Calorie (Nutritional) (4,186 J)
A calorie is a unit of energy. Various definitions exist but fall into two broad categories. The first, the small calorie, or gram calorie (symbol: cal), is defined as the amount of energy needed to raise the temperature of one gram of water by one degree Celsius at a pressure of one atmosphere. The second, the large calorie or kilogram calorie (symbols: Cal, kcal), also known as the food calorie and similar names, is defined in terms of the kilogram rather than the gram. It is equal to 1000 small calories or 1 kilocalorie (symbol: kcal). In a nutritional context, the kilojoule (kJ) is the SI unit of food energy, although the kilocalorie is still in common use. The word calorie is popularly used with the number of kilocalories of nutritional energy measured. As if to avoid confusion, it is sometimes written Calorie (with a capital "C") in an attempt to make the distinction, although this is not widely understood. Capitalization contravenes the rule that the initial letter of a unit name or its derivative shall be lower case in English.

Kilogram calorie (4,185 J)
A calorie is a unit of energy. Various definitions exist but fall into two broad categories. The first, the small calorie, or gram calorie (symbol: cal), is defined as the amount of energy needed to raise the temperature of one gram of water by one degree Celsius at a pressure of one atmosphere. The second, the large calorie or kilogram calorie (symbols: Cal, kcal), also known as the food calorie and similar names, is defined in terms of the kilogram rather than the gram. It is equal to 1000 small calories or 1 kilocalorie (symbol: kcal).

Watthour (3,600 J)
The watt hour (symbol Wh) is a unit of energy equal to 3.6 kilojoules. If energy is transmitted or used at a constant rate (power) over a period of time, the total energy in watt hours is equal to the power in watts multiplied by the time in hours. The kilowatt hour is commonly used as a billing unit for energy delivered to consumers by electric utilities.

Btu (1055 J)
The British thermal unit (Btu or BTU) is a traditional unit of heat; it is defined as the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. It is part of the United States customary units. Its counterpart in the metric system is the calorie, which is defined as the amount of heat required to raise the temperature of one gram of water by one degree Celsius. Heat is now known to be equivalent to energy, for which the SI unit is the joule; one BTU is about 1055 joules. While units of heat are often supplanted by energy units in scientific work, they are still important in many fields. As examples, in the United States the price of natural gas is quoted in dollars per million BTUs.

Kilojoule (1,000 J)
The joule (/dʒuːl/; symbol: J) is a derived unit of energy in the International System of Units. It is equal to the energy transferred to (or work done on) an object when a force of one newton acts on that object in the direction of its motion through a distance of one metre (1 newton metre or N⋅m). It is also the energy dissipated as heat when an electric current of one ampere passes through a resistance of one ohm for one second. It is named after the English physicist James Prescott Joule (1818–1889).

Liter atmosphere (101.325 J)
A unit of energy equal to the work done on a piston by a fluid at a pressure of 1 standard atmosphere (101,325 pascals) when the piston sweeps out a volume of 1 liter; equal to 101.325 joules.

Calorie (15°C) (4.19 J)
A calorie is a unit of energy. Various definitions exist but fall into two broad categories. The first, the small calorie, or gram calorie (symbol: cal), is defined as the amount of energy needed to raise the temperature of one gram of water by one degree Celsius at a pressure of one atmosphere. The second, the large calorie or kilogram calorie (symbols: Cal, kcal), also known as the food calorie and similar names, is defined in terms of the kilogram rather than the gram. It is equal to 1000 small calories or 1 kilocalorie (symbol: kcal). The amount of energy required to warm one gram of airfree water from 14.5 to 15.5 °C at standard atmospheric pressure. Experimental values of this calorie ranged from 4.1852 to 4.1858 J. The CIPM in 1950 published a mean experimental value of 4.1855 J, noting an uncertainty of 0.0005 J.

Calorie (I.T.) (4.19 J)
A calorie is a unit of energy. Various definitions exist but fall into two broad categories. The first, the small calorie, or gram calorie (symbol: cal), is defined as the amount of energy needed to raise the temperature of one gram of water by one degree Celsius at a pressure of one atmosphere. The second, the large calorie or kilogram calorie (symbols: Cal, kcal), also known as the food calorie and similar names, is defined in terms of the kilogram rather than the gram. It is equal to 1000 small calories or 1 kilocalorie (symbol: kcal). 1.163 mW·h = 4.1868 J exactly. This definition was adopted by the Fifth International Conference on Properties of Steam (London, July 1956).

Calorie (Thermochemical) (4.19 J)
A calorie is a unit of energy. Various definitions exist but fall into two broad categories. The first, the small calorie, or gram calorie (symbol: cal), is defined as the amount of energy needed to raise the temperature of one gram of water by one degree Celsius at a pressure of one atmosphere. The second, the large calorie or kilogram calorie (symbols: Cal, kcal), also known as the food calorie and similar names, is defined in terms of the kilogram rather than the gram. It is equal to 1000 small calories or 1 kilocalorie (symbol: kcal). In other scientific contexts, the term calorie almost always refers to the small calorie. Even though it is not an SI unit, it is still used in chemistry. For example, the energy released in a chemical reaction per mole of reagent is occasionally expressed in kilocalories per mole. Typically, this use was largely due to the ease with which it could be calculated in laboratory reactions, especially in aqueous solution: a volume of reagent dissolved in water forming a solution, with concentration expressed in moles per liter (1 liter weighing 1 kg), will induce a temperature change in degrees Celsius in the total volume of water solvent, and these quantities (volume, molar concentration and temperature change) can then be used to calculate energy per mole. It is also occasionally used to specify energy quantities that relate to reaction energy, such as enthalpy of formation and the size of activation barriers. However, its use is being superseded by the SI unit, the joule, and multiples thereof such as the kilojoule.

Gram calorie (4.19 J)
A calorie is a unit of energy. Various definitions exist but fall into two broad categories. The first, the small calorie, or gram calorie (symbol: cal), is defined as the amount of energy needed to raise the temperature of one gram of water by one degree Celsius at a pressure of one atmosphere. The second, the large calorie or kilogram calorie (symbols: Cal, kcal), also known as the food calorie and similar names, is defined in terms of the kilogram rather than the gram. It is equal to 1000 small calories or 1 kilocalorie (symbol: kcal). The amount of energy required to warm one gram of airfree water from 14.5 to 15.5 °C at standard atmospheric pressure. Experimental values of this calorie ranged from 4.1852 to 4.1858 J. The CIPM in 1950 published a mean experimental value of 4.1855 J, noting an uncertainty of 0.0005 J.

Foot pound (1.36 J)
The foot poundforce (symbol: ft⋅lbf or ft⋅lb) is a unit of work or energy in the Engineering and Gravitational Systems in United States customary and imperial units of measure. It is the energy transferred upon applying a force of one poundforce (lbf) through a linear displacement of one foot. The corresponding SI unit is the joule. The footpound is often used to specify the muzzle energy of a bullet in small arms ballistics, particularly in the United States.

Joule (1 J)
The joule (/dʒuːl/; symbol: J) is a derived unit of energy in the International System of Units. It is equal to the energy transferred to (or work done on) an object when a force of one newton acts on that object in the direction of its motion through a distance of one metre (1 newton metre or N⋅m). It is also the energy dissipated as heat when an electric current of one ampere passes through a resistance of one ohm for one second. It is named after the English physicist James Prescott Joule (1818–1889).

Newton meter (1 J)
The newton metre (also newtonmetre, symbol N m or N⋅m) is a unit of torque (also called moment) in the SI system. One newton metre is equal to the torque resulting from a force of one newton applied perpendicularly to the end of a moment arm that is one metre long. It is also used less commonly as a unit of work, or energy, in which case it is equivalent to the more common and standard SI unit of energy, the joule. In this usage the metre term represents the distance travelled or displacement in the direction of the force, and not the perpendicular distance from a fulcrum as it does when used to express torque. This usage is generally discouraged, since it can lead to confusion as to whether a given quantity expressed in newton metres is a torque or a quantity of energy. However, since torque represents energy transferred or expended per angle of revolution, one newton metre of torque is equivalent to one joule per radian.

Wattsecond (1 J)
A watt second (also wattsecond, symbol Ws) is a derived unit of energy equivalent to the joule. The wattsecond is the energy equivalent to the power of one watt sustained for one second. While the wattsecond is equivalent to the joule in both units and meaning, there are some contexts in which the term "wattsecond" is used instead of "joule". The kilowatt hour (kWh) is equivalent to 3,600,000 wattseconds and is a unit used in the electricity market, and by producers of electricity. Although joule and wattsecond mean exactly the same thing (they represent the same amount of the same physical quantity, viz. energy), the newton metre is not equivalent to the joule (despite having the same dimensions) as it represents torque rather than energy. (In terms of vectors, torque is a cross product of force and distance, and energy is their dot product.)

Inch pound (0.113 J)
A unit of work equal to the work done in raising one pound against the force of gravity through a distance of one inch.

Inch ounce (0.0071 J)
A unit of work equal to the work done in raising one ounce against the force of gravity through a distance of one inch.

Millijoule (0.001 J)
The millijoule (mJ) is equal to one thousandth (10⁻³) of a joule.

Microjoule (0.000001 J)
The microjoule (μJ) is equal to one millionth (10⁻⁶) of one joule. The Large Hadron Collider (LHC) produces collisions of the microjoule order (7 TeV) per particle.

Teraelectronvolt (0.00000016 J)
In physics, the electronvolt (symbol eV, also written electronvolt and electron volt) is a unit of energy equal to approximately 1.6×10−19 joules (symbol J) in SI units. By definition, it is the amount of energy gained (or lost) by the charge of a single electron moving across an electric potential difference of one volt. Hence, it has a value of one volt, 1 J/C, multiplied by the electron's elementary charge e, 1.6021766208(98)×10−19 C. Therefore, one electronvolt is equal to 1.6021766208(98)×10−19 J. The electronvolt is not a SI unit, and its definition is empirical (unlike the litre, the lightyear and other such nonSI units), where its value in SI units must be obtained experimentally.

Erg (0.0000001 J)
The erg is a unit of energy and work equal to 10⁻⁷ joules. It originated in the centimetre–gram–second (CGS) system of units. It has the symbol erg. The erg is not an SI unit. Its name is derived from ergon (’έργον) a Greek word meaning work or task. An erg is the amount of work done by a force of one dyne exerted for a distance of one centimeter. In the CGS base units, it is equal to one gram centimetersquared per secondsquared (g·cm2/s2). It is thus equal to 10−7 joules or 100 nanojoules (nJ) in SI units. An erg is approximately the amount of work done (or energy consumed) by one common house fly performing one "push up," the legbending dip that brings its mouth to the surface on which it stands and back up.

Nanojoule (0.000000001 J)
The nanojoule (nJ) is equal to one billionth (10⁻⁹) of one joule. 160 nanojoules is about the kinetic energy of a flying mosquito.

Picojoule (0.000000000001 J)
The Picojoule (pJ) is equal to one trillionth (10⁻¹²) of one joule.

Megaelectronvolt (0.00000000000016 J)
In physics, the electronvolt (symbol eV, also written electronvolt and electron volt) is a unit of energy equal to approximately 1.6×10−19 joules (symbol J) in SI units. By definition, it is the amount of energy gained (or lost) by the charge of a single electron moving across an electric potential difference of one volt. Hence, it has a value of one volt, 1 J/C, multiplied by the electron's elementary charge e, 1.6021766208(98)×10−19 C. Therefore, one electronvolt is equal to 1.6021766208(98)×10−19 J. The electronvolt is not a SI unit, and its definition is empirical (unlike the litre, the lightyear and other such nonSI units), where its value in SI units must be obtained experimentally.

Femtojoule (0.000000000000001 J)
The joule (/dʒuːl/; symbol: J) is a derived unit of energy in the International System of Units. It is equal to the energy transferred to (or work done on) an object when a force of one newton acts on that object in the direction of its motion through a distance of one metre (1 newton metre or N⋅m). It is also the energy dissipated as heat when an electric current of one ampere passes through a resistance of one ohm for one second. It is named after the English physicist James Prescott Joule (1818–1889).

Hartree (0.0000000000000000043 J)
The hartree (symbol: Eh or Ha), also known as the Hartree energy, is the atomic unit of energy, named after the British physicist Douglas Hartree. It is defined as 2R∞hc, where R∞ is the Rydberg constant, h is the Planck constant and c is the speed of light. The 2014 CODATA recommended value is Eh = 4.359 744 650(54)×10−18 J = 27.211 386 02(17) eV. The hartree energy is approximately the electric potential energy of the hydrogen atom in its ground state and, by the virial theorem, approximately twice its ionization energy; the relationships are not exact because of the finite mass of the nucleus of the hydrogen atom and relativistic corrections. The hartree is usually used as a unit of energy in atomic physics and computational chemistry: for experimental measurements at the atomic scale, the electronvolt (eV) or the reciprocal centimetre (cm−1) are much more widely used.

Electronvolt (0.00000000000000000016 J)
In physics, the electronvolt (symbol eV, also written electronvolt and electron volt) is a unit of energy equal to approximately 1.6×10−19 joules (symbol J) in SI units. By definition, it is the amount of energy gained (or lost) by the charge of a single electron moving across an electric potential difference of one volt. Hence, it has a value of one volt, 1 J/C, multiplied by the electron's elementary charge e, 1.6021766208(98)×10−19 C. Therefore, one electronvolt is equal to 1.6021766208(98)×10−19 J. The electronvolt is not a SI unit, and its definition is empirical (unlike the litre, the lightyear and other such nonSI units), where its value in SI units must be obtained experimentally.