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Unit system  SI derived unit 
Unit of  Energy 
Symbol  J 
Named after  James Prescott Joule 
1 J in...  is equal to... 
SI base units  1 kg·m^{2}/s^{2} 
CGS units  1×10^{7} erg 
kilowatt hours  2.78×10^{−7} kW⋅h 
kilocalories  2.39×10^{−4} kcal 
BTUs  9.48×10^{−4} BTU 
electronvolts  6.24×10^{18} eV 
Unit system  SI derived unit 
Unit of  Energy 
Symbol  J 
Named after  James Prescott Joule 
1 J in...  is equal to... 
SI base units  1 kg·m^{2}/s^{2} 
CGS units  1×10^{7} erg 
kilowatt hours  2.78×10^{−7} kW⋅h 
kilocalories  2.39×10^{−4} kcal 
BTUs  9.48×10^{−4} BTU 
electronvolts  6.24×10^{18} eV 
The joule (/ˈdʒuːl/ or sometimes /ˈdʒaʊl/), symbol J, is a derived unit of energy, work, or amount of heat in the International System of Units.^{[1]} It is equal to the energy expended (or work done) in applying a force of one newton through a distance of one metre (1 newton metre or N·m), or in passing an electric current of one ampere through a resistance of one ohm for one second. It is named after the English physicist James Prescott Joule (1818–1889).^{[2]}^{[3]}^{[4]}
In terms firstly of base SI units and then in terms of other SI units:
where kg is the kilogram, m is the metre, s is the second, N is the newton, Pa is the pascal, W is the watt, C is the coulomb, and V is the volt.
One joule can also be defined as:
This SI unit is named after James Prescott Joule. As with every International System of Units (SI) unit whose name is derived from the proper name of a person, the first letter of its symbol is upper case (J). However, when an SI unit is spelled out in English, it should always begin with a lower case letter (joule), except in a situation where any word in that position would be capitalized, such as at the beginning of a sentence or in capitalized material such as a title. Note that "degree Celsius" conforms to this rule because the "d" is lowercase.— Based on The International System of Units, section 5.2.
In angular mechanics, torque is analogous to the linear Newtonian mechanics parameter of force, moment of inertia to mass, and angle to distance. Energy is the same in both systems. Thus, although the joule has the same dimensions as the newtonmetre (1 J = 1 N·m = 1 kg·m^{2}·s^{−2}), these units are not interchangeable: the CGPM has given the unit of energy the name "joule", but has not given the unit of torque any special name, hence the unit of torque is known as the newtonmetre (N·m)  a compound name derived from its constituent parts.^{[5]} Torque and energy are related to each other using the equation
where E is the energy, τ is the torque, and θ is the angle moved (in radians). Since radians are dimensionless, it follows that torque and energy have the same dimensions.
The use of newtonmetres for torque and joules for energy is useful in helping avoid misunderstandings and miscommunications.^{[5]}
An additional solution is to realize that joules are scalars – they are the dot product of a vector force and a vector displacement whereas torque is a vector. Torque is the cross product of a distance vector and a force vector. Drawing a traditional vector arrow over "newtonmetre" in a torque resolves the ambiguity.
One joule in everyday life represents approximately:
Since the joule is also a wattsecond and the common unit for electricity sales to homes is the kW·h (kilowatthour), a kW·h is thus 1000 (kilo) × 3600 seconds = 3.6 MJ (megajoules).

The nanojoule (nJ) is equal to one billionth of one joule. One nanojoule is about 1/160 of the kinetic energy of a flying mosquito.^{[9]}
The microjoule (μJ) is equal to one millionth of one joule. The Large Hadron Collider (LHC) is expected to produce collisions on the order of 1 microjoule (7 TeV) per particle.
The millijoule (mJ) is equal to one thousandth of a joule.
The kilojoule (kJ) is equal to one thousand (10^{3}) joules. Nutritional food labels in certain countries express energy in standard kilojoules (kJ).
One kilojoule per second (1 kilowatt) is approximately the amount of solar radiation received by one square metre of the Earth in full daylight.^{[10]}
The megajoule (MJ) is equal to one million (10^{6}) joules, or approximately the kinetic energy of a onetonne vehicle moving at 160 km/h (100 mph).
Because 1 watt times 1 second equals 1 joule, 1 kilowatthour is 1000 watts times 3600 seconds, or 3.6 megajoules.
The gigajoule (GJ) is equal to one billion (10^{9}) joules. 6 GJ is about the amount of potential chemical energy in a barrel of oil, when combusted.^{[11]}
The terajoule (TJ) is equal to one trillion (10^{12}) joules. About 63 TJ of energy was released by the atomic bomb that exploded over Hiroshima.^{[12]} The International Space Station, with a mass of approximately 450,000 kg and orbital velocity of 7.7 km/s,^{[13]} has a kinetic energy of roughly 13 TJ.
The petajoule (PJ) is equal to one quadrillion (10^{15}) joules. 210 PJ is equivalent to about 50 megatons of TNT. This is the amount of energy released by the Tsar Bomba, the largest manmade nuclear explosion ever.
The exajoule (EJ) is equal to one quintillion (10^{18}) joules. The 2011 Tōhoku earthquake and tsunami in Japan had 1.41 EJ of energy according to its 9.0 on the moment magnitude scale. Energy in the United States used per year is roughly 94 EJ.
The zettajoule (ZJ) is equal to one sextillion (10^{21}) joules. Annual global energy consumption is approximately 0.5 ZJ.
The yottajoule (YJ) is equal to one septillion (10^{24}) joules. This is approximately the amount of energy required to heat the entire volume of water on Earth by 1 °C.
1 joule is equal to:
Units defined exactly in terms of the joule include:

