How to size skimmer properly

[BeccaMel]

I have a 120 gallon display tank and a 40 gallon tank as my sump system. I plan to use filter floss on top of live rock for one section, a small compartment for my heaters and refugium, one for my protein skimmer, then finally an area for the return pump. I have done a lot of research on how to size skimmers but I don’t understand if I’m supposed to include the sump size in my calculations or not

 

[Mr. Mojo Rising]

I include sump size in my calculations. If it were me, I would get something in the 200 gallon range, more is often better. Everything on my tanks are rated for higher