**Loop gain** is a measure of the gain of a system controlled by feedback loops. As such, the concept of loop gain is useful in a variety of disciplines. Traditionally, most of those have been in the fields of electronics, telecommunications, or (electronic or non-electronic) control systems. It is also useful in biology.

In amplifiers with feedback, loop gain is the product of the gain in the feedback loop and the feedback factor in that loop.

In telecommunications, loop gain can be either of:

- The total usable power gain of a carrier terminal or two-wire repeater. The maximum usable gain is determined by, and may not exceed, the losses in the closed path.
- The sum of the gains, expressed in dB, acting on a signal passing around a closed path,
*i.e.*, a loop.

This article incorporates public domain material from the General Services Administration document "Federal Standard 1037C" (in support of MIL-STD-188).

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