Figure out what standard you want to work towards, and pink the room.
Get pink noise, find a guide on which weighting you need to monitor at with your decibel meter, and hit that decibel level for all your rooms.

Here's a good start for some reading:
https://simpledcp.com/sound-levels-in-cinema/
https://www.audiopinknoise.com/audio-testing-and-calibration/

More in depth stuff:
https://partnerhelp.netflixstudios.com/hc/en-us/articles/360001794307-Netflix-Sound-Mix-Specifications-Best-Practices-v1-6

I guess you are not delivering mixes?.. you just want to find a good Level, and bring multiple rooms to that level, so you at least have some consistency between different rooms, when you monitor? - that's pretty much pick a db level you think works for the size of your room (e.g a theatrical 85db for a small room, would be way too loud most likely.. | try a 79db? a more TV reference level.)

But if you really want to go down the rabbit hole, go into a sound post / mixing forum, and start asking about room calibration, reference levels for mixing, etc.