Measure room ambient noise how too

[Harrycr]

Hi
I am trying to get reliable measurements.
I would like to know how to measure above the room noise e. g road noise, refrigerator noise etc.
Do I use SPL or is this not the best way?
I believe measure 20-30db above.

Thanks

 

[John Mulcahy]

Just measure at around 75 dB.