dBm

A dBm is a standard unit for measuring levels of power in relation to a 1 milliwatt reference signal.

dBm is similar to dB, or decibel, except that where dB is relative to the power of the input signal, dBm always relates to a 1 milliwatt signal.

In other words, dB is a relative measurement and dBm is an absolute measurement.

A minus sign before the dBm indicates a loss and a plus sign or no sign at all before the dBm indicates a gain.

The dBm Formula

The dBm value of a signal can be expressed utilizing the following algorithm:

db = log₁₀ Signal Power / .001 watt