dBm is the power ratio of measured power referenced to 1 milliwatt (mW) in decibels (dB).
A change in power ratio by a factor of 10 is a 10 dB change.
A change in power ratio by a factor of 2 is approximately a 3 dB change.
Voltage across 50 load, at 10dBm –> 1V
For every 10x in voltage, power increases by 20dB.