Editing Efficiency (section)

== 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]] 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]] of [[heat engine]]s in [[thermodynamics]], 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]], ''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).