What is the formula used to convert dBm to dB?

The correct approach for converting dBm to dB involves understanding that dBm is a logarithmic measure of power relative to 1 milliwatt. When considering the change in power levels, the formula to find the difference in decibels (dB) between two power levels expressed in dBm involves subtraction.

Specifically, if you have two power levels, one expressed as dBm in and the other as dBm out, finding the change in power level from one to the other is done by taking the dBm out value and subtracting the dBm in value from it. This operation gives the delta in decibels, which indicates whether the power has increased or decreased.

This methodology adheres to the principles of logarithmic scale calculations, where the difference in levels (in decibels) corresponds to the ratio of the two power levels. Therefore, to obtain the change in power represented in dB, subtracting the input level from the output level is correct.