There is not a specific amount of square footage that the can covers as it is used as a spot application. You should get 1.5 to 2 gallons of foam per can of Foam Fresh since it is a very dry, high expansion foam.
Foam Fresh is a 20:1 ratio, very dry. Delivers approx 1.5-2 gals Foam/ can.
Foam Fresh Ordor Control Foam can be used in sink drains, but foaming products will only go so far down. If the odor is coming from somewhere beyond the p trap it may not be effective.