In case of reference-related dBs, dB is defined as 10∙log(P/Pref) or 20∙log(V/Vref). In the table below you find the most commonly used dBs.
|dBV||Vref = 1VRMS||dBV = 20∙log(V/1VRMS)|
|dBW||Pref = 1W||dBW = 10∙log(P/1W)|
|dBj||Vref = 1mVRMS||dBj = 20∙log(V/1mVRMS)|
|dBm||Pref = 1mW||dBm = 10∙log(P/1mW)|
|dBu (=dBv)||Vref = √0.6V = 0.775VRMS (0.6V is the voltage across a 600 ohm resistor dissipating 1mW)||dBu = 20∙log(V/0.775VRMS)|
Examples: 0dBV = 1V = 60dBj; 0dBW = 1W = 30dBm.