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Energy units converter. Converts joules, calories, many physical, british, american and time related units.
Some facts
  • Energy is the scalar physical quantity expressing the ability to do the work.
  • Energy is additive. This means that the total energy of the system consisting of the N objects, is the sum of the energy of each of the bodies.
  • The kinetic energy is work to be done in order to provide the body with mass m, velocity V. It amounts to Ekinetic = mV2/2, where Ekinetic is the kinetic energy, m is the mass, and V is the value of the velocity vector.
  • The potential energy at the point x0 is work to be done to put the body at this point (moving them from infinity).

    • There are many different symbols used for potential energy depending on kind of science. Most common are U, V, or simply Epot..
    • Potential energy can be negative. This means that we don't need to perform the work to put the body in the current positions at all, but also it is needed to do the work to corrupt current system. In this case we say that system is in a bound. A good example here are chemical molecules that are associated systems, because we need to do work to break chemical bonds.
    • The function U=f(x), which assigns value of potential energy to each point x is commonly called potential energy surface. Sometimes, when poeple want to mark that surface have more than 3 dimensions (degree of freedom), they use term hipersurface. The concept of (hiper)surface of potential energy is widely used for example in quantum chemistry or physics of the atomic nucleus.
  • There are many forms of energy for example: heat or electrical.
  • The basic energy unit in SI system is 1J (one jul), so it's the same as unit of work. However, for practical reasons many different units are used depending on kind of science for example:

    • elektronovolts (eV) in high-energy physics,
    • atomic units (au) in quantum chemistry,
    • calories in dietetic,
    • horsepower in automotive industry.
  • The average kinetic energy of single particle divided by the number of degrees of freedom is temperature of the system. Such concepts owe the development of statistical thermodynamics (physics), which made it possible to link the micro state (individual particles level) with macroscopic quantities (such as temperature, pressure). Previously, the concept of micro and macroscopic were independent. It is worth noting that the concept of temperature has only statistical meaning. This means for example that temperature for single particle has no meaning.
  • One of the fundamental laws of nature is the desire to minimize energy. There are no known causes of this fact, but an enormous amount of physical theory is based on this postulate. Very often the solution to a practical problem boils down to mininimalization energy problem. Examples include:

    • Molecular mechanics - the way of finding optimal molecule geometry using clasical Newton dynamic.
    • Variational methods - the set of general methods, that searches for wave functions, for which the system gives minimal average energy (formally the average value of the Hamiltonian). Good examples are Hartree-fock equations, which (together with Density Functional Theory - DFT) are the foundations of modern quantum-mechanical calculations.
    • Chemical reaction paths - sets of methods trying to search for optimal trace on energy surface.
    A common feature of all of the above examples, it is asking "what to do to reach a minimum of energy."
    From a mathematical point of view, that are classic optimization problems. Mathematical apparatus that deals with this kind of problem is - depending on whether we are looking for the numbers or functions - calculus or calculus of variations.
  • If we have the potential energy surface, we can get forces that operate in various points in the system. To do this we need to calculate the energy derivative dE/dx in point. This fact is due to the reversal of the definition of work (integral of the product of the displacement and the applied force). Such a procedure may be used for numerical optimization of the geometry of the system. To do this we need to repeat in loop (as long as there are forces in the system):

    • Compute forces working for each particle (by computing derivate dE/dx).
    • Move particles by computed forces.
    Above procedure is widely used in many numerical simulations for example in quantum chemistry.
How to convert?
  • Enter the number to field "value" - enter the NUMBER only, no other words, symbols or unit names. You can use dot (.) or comma (,) to enter fractions.
    • 1000000
    • 123,23
    • 999.99999
  • Find and select your starting unit in field "unit". Some unit calculators have huge number of different units to select from - it's just how complicated our world is...
  • And... you got the result in the table below. You'll find several results for many different units - we show you all results we know at once. Just find the one you're looking for.
value: unit: decimals:

common use

joule [J]
calorie [cal]
kilo-calorie [kcal]
kilowatt-hour [kW·h]

metric (SI)

yottajoule [YJ]
zettajoule [ZJ]
exajoule [EJ]
petajoule [PJ]
terajoule [TJ]
gigajoule [GJ]
megajoule [MJ]
kilojoule [kJ]
hectojoule [hJ]
decajoule [daJ]
joule [J]
decijoule [dJ]
centijoule [cJ]
millijoule [mJ]
microjoule [µJ]
nanojoule [nJ]
picojoule [pJ]
femtojoule [fJ]
attojoule [aJ]
zeptojoule [zJ]
yoctojoule [yJ]


British thermal unit (thermochemical) [BTUth]
British thermal unit (ISO) [BTUISO]
British thermal unit (63 °F) [BTU63 °F]
British thermal unit (60 °F) [BTU60 °F]
British thermal unit (59 °F) [BTU59 °F]
British thermal unit (International Table) [BTUIT]
British thermal unit (mean) [BTUmean]
British thermal unit (39 °F) [BTU39]
cubic foot of atmosphere [cu ft atm; scf]
cubic yard of atmosphere [cu yd atm; scy]
cubic foot of natural gas
foot-poundal [ft pdl]
foot-pound force [ft lbf]
gallon-atmosphere (US) [US gal atm]
gallon-atmosphere (imperial) [imp gal atm]
inch-pound force [in lbf]
therm (U.S.)
therm (E.C.)

calories related

calorie (20 °C) [cal20 °C]
calorie (thermochemical) [calth]
calorie (15 °C) [cal15 °C]
calorie (International Table) [calIT]
calorie (mean) [calmean]
calorie (3.98 °C) [cal3.98 °C]
kilocalorie; large calorie [kcal; Cal]


atomic unit of energy [au]
Celsius heat unit (International Table) [CHUIT]
cubic centimetre of atmosphere; standard cubic centimetre [cc atm; scc]
electronvolt [eV]
erg (cgs unit) [erg]
litre-atmosphere [l atm]
hartree [Eh]
rydberg [Ry]
thermie [th]

time related

horsepower-hour [hp·h]
watt-second [W·s]
watt-hour [W·h]
kilowatt-second [kW·s]
kilowatt-hour [kW·h]

materials related

barrel of oil equivalent [bboe]
ton of TNT [tTNT]
ton of coal equivalent [TCE]
ton of oil equivalent [TOE]
energy · cal · kcal · calories

Tags to Polish version:
energia · kalorie