"Caveat Lector" wrote
dB is a ratio for example dB = 10 log10 (P1/P2)
....snip...
In the equation above P2 is always one milliwatt
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To elaborate, P2 above must be 1 mW only if one wants to calculate dBm.

The equation as it is written above will calculate the relationship in
decibels between any two power values expressed in the same units. For
example, to find the gain of an amplifier in decibels when its input power
is 50 watts and its output power is 1.2 kW:

dB = 10*log(1200/50) = 10*log(24) = 10*1.38 = 13.8

RF