FB to CC Ratio

I'm a newbie here planning to build an outdoor kitchen which will of course include a smoker.  I saw some references in other posts regarding FB to CC size charts/formulas.  This is why I am here because I would never have known there was such a requirement.  Can someone please steer me to this information?  Haven't determined the size's of anything yet, but this will definitely come in handy when I start the process.

Thanks in advance....