How far can I drive my car with a gallon of fuel ?
It really is exactly the same thing, it depends on your exact set up not so much on the fuel used.
With my Caldera Cone 550ml pot, I boil 60f water in about 6:30min with about 1/2 oz of 95% Ethanol.
Now change any of those specs and at best you will use a fraction less (using a wider pot, everything else the same ) at worst you will burn three/four times as much fuel
(20f, narrower pot,no windscreen,wide flame burner...)
The trick with alcohol is to have a system, that is use a burner/pot/windscreen and fuel combo designed to work as a kit.