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 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.
Foam Fresh is a 20:1 ratio, very dry. Delivers approx 1.5-2 gals Foam/ can.