Carb sizing question?

[greenmachine]

If say, you have a 20mm carb or a 30mm carb. What is the difference? What gives you that #? What do you have to modify to change upsize on a carb? This question pertains to mini quads.

[TRX450R_Racer]

It will be larger where the air box boot & intake boot slide on. Not sure about the internals.