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Efficiency is the (often measurable) ability to avoid wasting materials, energy, efforts, money, and time in doing something or in producing a desired result. In a more general sense, it is the ability to do things well, successfully, and without waste. "Efficiency is thus not a goal in itself. It is not something we want for its own sake, but rather because it helps us attain more of the things we value". In more mathematical or scientific terms, it signifies the level of performance that uses the least amount of inputs to achieve the highest amount of output. It often specifically comprises the capability of a specific application of effort to produce a specific outcome with a minimum amount or quantity of waste, expense, or unnecessary effort. Sickles, R., and Zelenyuk, V. (2019). Measurement of Productivity and Efficiency: Theory and Practice. Cambridge: Cambridge University Press. doi:10.1017/9781139565981
/ref> Efficiency refers to very different inputs and outputs in different fields and industries.

Efficiency and effectiveness

Efficiency is very often confused with
effectiveness Effectiveness is the capability of producing a desired result or the ability to produce desired output. When something is deemed effective, it means it has an intended or expected outcome, or produces a deep, vivid impression. Etymology The origi ...
. In general, efficiency is a measurable concept, quantitatively determined by the
ratio In mathematics, a ratio indicates how many times one number contains another. For example, if there are eight oranges and six lemons in a bowl of fruit, then the ratio of oranges to lemons is eight to six (that is, 8∶6, which is equivalent to ...

of useful output to total useful input. Effectiveness is the simpler concept of being able to achieve a desired result, which can be expressed quantitatively but does not usually require more complicated mathematics than addition. Efficiency can often be expressed as a percentage of the result that could ideally be expected, for example if no energy were lost due to friction or other causes, in which case 100% of fuel or other input would be used to produce the desired result. In some cases efficiency can be indirectly quantified with a non-percentage value, e.g.
specific impulse Specific impulse (usually abbreviated ) is a measure of how efficiently a reaction mass engine (a rocket engine, rocket using propellant or a jet engine using fuel) creates thrust. For engines whose reaction mass is only the fuel they carry, speci ...
. A common but confusing way of distinguishing between efficiency and effectiveness is the saying "Efficiency is doing things right, while effectiveness is doing the right things." This saying indirectly emphasizes that the selection of objectives of a production process is just as important as the quality of that process. This saying popular in business however obscures the more common sense of "effectiveness", which would/should produce the following mnemonic: "Efficiency is doing things right; effectiveness is getting things done." This makes it clear that effectiveness, for example large production numbers, can also be achieved through inefficient processes if, for example, workers are willing or used to working longer hours or with greater physical effort than in other companies or countries or if they can be forced to do so. Similarly, a company can achieve effectiveness, for example large production numbers, through inefficient processes if it can afford to use more energy per product, for example if energy prices or labor costs or both are lower than for its competitors.

Mathematical expression

Efficiency is often measured as the ratio of useful output to total input, which can be expressed with the mathematical formula ''r''=''P''/''C'', where ''P'' is the amount of useful output ("product") produced per the amount ''C'' ("cost") of resources consumed. This may correspond to a percentage if products and
consumables Consumables (also known as consumable goods, non-durable goods, or soft goods) are goods that are intended to be consumed. People have, for example, always consumed food and water. Consumables are in contrast to durable goods. Disposable products ...
are quantified in compatible units, and if consumables are transformed into products via a conservative process. For example, in the analysis of the
energy conversion efficiency Energy conversion efficiency (''η'') is the ratio In mathematics, a ratio indicates how many times one number contains another. For example, if there are eight oranges and six lemons in a bowl of fruit, then the ratio of oranges to lemons i ...
of
heat engine In thermodynamics and engineering, a heat engine is a system that converts heat to mechanical energy, which can then be used to do work (physics), mechanical work. It does this by bringing a working substance from a higher state temperature to ...

s in
thermodynamics Thermodynamics is a branch of physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order of nature, or, in ot ...

, the product ''P'' may be the amount of useful work output, while the consumable ''C'' is the amount of high-temperature heat input. Due to the
conservation of energy In physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order of nature, or, in other words, to the regular s ...
, ''P'' can never be greater than ''C'', and so the efficiency ''r'' is never greater than 100% (and in fact must be even less at finite temperatures).

In science and technology

In physics

* Useful work per quantity of energy, mechanical advantage over ideal mechanical advantage, often denoted by the Greek lowercase letter η (
Eta Eta (uppercase , lowercase ; grc, ἦτα ''ē̂ta'' or ell, ήτα ''ita'' ) is the seventh letter of the Greek alphabet The Greek alphabet has been used to write the Greek language since the late ninth or early eighth century BC. It is ...

): **
Electrical efficiency The efficiency of a system in electronics Electronics comprises the physics, engineering, technology and applications that deal with the emission, flow and control of electrons in vacuum and matter. It uses active devices to control electron fl ...
**
Energy conversion efficiency Energy conversion efficiency (''η'') is the ratio In mathematics, a ratio indicates how many times one number contains another. For example, if there are eight oranges and six lemons in a bowl of fruit, then the ratio of oranges to lemons i ...
**
Mechanical efficiency Mechanical efficiency is a dimensionless number that measures the effectiveness of a machine A machine is a man-made device that uses power to apply forces and control movement to perform an action. Machines can be driven by animals and peo ...
**
Thermal efficiency In thermodynamics Thermodynamics is a branch of physics that deals with heat, Work (thermodynamics), work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these quan ...
, ratio of work done to thermal energy consumed *
Efficient energy use Efficient energy use, sometimes simply called energy efficiency, is the goal to reduce the amount of energy required to provide products and services and can also reduce effects of air pollution. For example, insulating a building allows it to ...
, the objective of maximising efficiency ** In thermodynamics: ***
Energy conversion efficiency Energy conversion efficiency (''η'') is the ratio In mathematics, a ratio indicates how many times one number contains another. For example, if there are eight oranges and six lemons in a bowl of fruit, then the ratio of oranges to lemons i ...
, measure of second law thermodynamic loss **
Radiation efficiency In Antenna (radio), antenna theory, antenna efficiency is most often used to mean radiation efficiency. In the context of antennas, one often just speaks of "efficiency." It is a measure of the electrical efficiency with which a radio antenna con ...
, ratio of radiated power to power absorbed at the terminals of an antenna **
Volumetric efficiency Volumetric efficiency (VE) in internal combustion engine An internal combustion engine (ICE) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the workin ...
, in internal combustion engine design for the RAF *
Lift-to-drag ratio In aerodynamics, the lift-to-drag ratio (or L/D ratio) is the amount of Lift (force), lift generated by a wing or vehicle, divided by the aerodynamic drag it creates by moving through air. A greater or more favorable L/D ratio is typically one of th ...
*
Faraday efficiencyFaraday efficiency (also called ''faradaic efficiency'', ''faradaic yield'', ''coulombic efficiency'' or ''current efficiency'') describes the efficiency with which charge (electron The electron is a subatomic particle, symbol or , whose elect ...
, electrolysis *
Quantum efficiency In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that studies matter, its Motion (physics), motion and behavior through ...
, a measure of sensitivity of a photosensitive device *
Grating efficiencyDiffraction efficiency is the performance of diffractive optical elements – especially diffraction gratings – in terms of Power (physics), power throughput. It's a measure of how much optical power is diffracted into a designated directio ...
, a generalization of the reflectance of a mirror, extended to a diffraction grating

In economics

*
Productivity improving technologiesThe productivity-improving technologies are the technological innovations that have historically increased productivity Productivity describes various measures of the efficiency of production. Often, a productivity measure is expressed as the ra ...
*
Economic efficiency In , economic efficiency is, roughly speaking, a situation in which nothing can be improved without something else being hurt. Depending on the context, it is usually one of the following two related concepts: * or : any changes made to assist on ...
, the extent to which waste or other undesirable features are avoided *
Market efficiency The efficient-market hypothesis (EMH) is a hypothesis in financial economics Financial economics is the branch of economics Economics () is the social science that studies how people interact with value; in particular, the Production (ec ...
, the extent to which a given market resembles the ideal of a
efficient market
**
Pareto efficiency Pareto efficiency or Pareto optimality is a situation where no individual or preference criterion can be better off without making at least one individual or preference criterion worse off or without any loss thereof. The concept is named after Vi ...
, a state of its being impossible to make one individual better off, without making any other individual worse off ** Kaldor-Hicks efficiency, a less stringent version of Pareto efficiency **
Allocative efficiency Allocative efficiency is a state of the economy in which production is alligned with consumer preferences; in particular, every good or service is produced up to the point where the last unit provides a marginal benefit to consumers equal to the mar ...
, the optimal distribution of goods **
Efficiency wages The term efficiency wages (or rather "efficiency earnings") was introduced by Alfred Marshall to denote the wage per efficiency unit of labor. Marshallian efficiency wages would make employers pay different wages to workers who are of different effi ...
, paying workers more than the market rate for increased productivity *
Business efficiency The efficiency ratio indicates the expenses as a percentage of revenue (expenses / revenue), with a few variations – it is essentially how much a corporation or individual spends to make a dollar; entities are supposed to attempt minimizing effici ...
, revenues relative to expenses, etc. * Efficiency Movement, of the Progressive Era (1890–1932), advocated efficiency in the economy, society and government

In other sciences

* In computing: **
Algorithmic efficiency In computer science Computer science deals with the theoretical foundations of information, algorithms and the architectures of its computation as well as practical techniques for their application. Computer science is the study of Algori ...
, optimizing the speed and memory requirements of a computer program. ** Storage efficiency, effectiveness of computer data storage ** Efficiency factor, in data communications *
Efficiency (statistics) In the comparison of various statistical procedures, efficiency is a measure of quality of an estimatorIn statistics Statistics is the discipline that concerns the collection, organization, analysis, interpretation, and presentation of data. I ...
, a measure of desirability of an estimator *
Material efficiencyImage:BuildingSite.jpg, 250px, Building construction can be a materially consumptive endeavor. Material efficiency is a description or Metric (mathematics), metric which expresses the degree in which raw materials are consumed, incorporated, or waste ...
, compares material requirements between construction projects or physical processes * Administrative efficiency, measuring transparency within public authorities and simplicity of rules and procedures for citizens and businesses *
Photosynthetic efficiencyThe photosynthetic efficiency is the fraction of light energy converted into chemical energy during photosynthesis Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cell ...