Not that i’m aware of … you’d need to get probably empirical data using a test signal at various dBm levels for a certain gain you use on your specific SDR.
Then you’d need to set up a conversion somewhere in either the graphs1090 or dump1090-fa code.
Have fun with that 
Thanks, you can change colors by redefining them in /etc/default/graphs1090 … i suppose this needs some documentation
LGREEN=45d945
LBLUE=4f59e3
LCYAN=29a7e6
GREEN=32CD32
DGREEN=228B22
BLUE=0011EE
ABLUE=0022DD
DBLUE=0033AA
CYAN=00A0F0
RED=E30022
DRED=990000
LRED=FFCCCB
That’s from graphs1090.sh … you can redefine them in the config.
Be aware noise is just the average power for the time no messages are detected.
That means it includes undetected or messages that failed to decode as such it’s highly variable with band contention and overlapping messages which raise the noise.
All the other data you see is actually statistics on aircraft and their signal levels.
(while noise is a time average of the power of everything minus messages)
Also this is not the right thread, a new one or this one seem appropriate Graphs for dump1090 -- my version with install script
(but … it’s here now so whatever )