Gain

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In electronics, gain is the logarithm (base 10) of the ratio of signal output from a system to signal input to the system. A signal is usually measured in units of voltage or power gain.

An audio amplifier changing the 1 volt at the input to 10 volts at the output has a gain of 20 dB. That is 20 · log (10/1).

The ratio is often expressed in decibels (dB).

For example, if output=500mW and input=5mW then

gain=500/5 = 100 = 2B (bel) or 20dB

In antenna design, gain is the logarithm of the ratio of the antenna's radiation pattern to that of some ideal antenna, typically the theoretical isotropic antenna.

In finance, gain is profit or increase in value of an investment such as stock and bond. Gain is calculated by fair market value or proceed from sale of the investment minus the sum of purchase price and all costs associated with it. If the investment is not converted into cash or another asset the gain is called unrealized gain.

In psychology, primary gain and secondary gain are commonly seen in Somatoform Disorders.