# Voltage gain - simplified formula (for equal impedances)

## Description

The power gain can be calculated using voltage instead of power using Joule’s first law to calculate a voltage gain. In many cases, the input and output impedances are equal.

This simplified formula, the 20 log rule, is used to calculate a voltage gain in decibels and is equivalent to a power gain only if the impedances at input and output are equal.

Related formulas## Variables

gain_{dB} | Voltage gain (dB) (dimensionless) |

V_{out} | Output voltage (dimensionless) |

V_{in} | Input voltage (dimensionless) |