Db power value

In the Y axis of the attached picture, it shows a “dB” level, I want to
know if this is the real value of the captured signal (dB).
I want to convert it into a power level ‘mW’ (10^(dBm/10)). I thought it
could be dBfs (dB full scale) and I’m not quite sure if it’s the
absolute power level or dBfs.
Is there any way in the GRC, to show me a numerical value? or I just
have to look and compare the plot in Y axis. Any suggestion is welcome.