For every 1 US Gallon of liquid there are 128 ounces which makes up that gallon of liquid.
So to find out how many 12 oz cups of liquid it takes to make a gallon of liquid you would take 12 and multiply that 12 ounces by 11 which would mean you would get 132 ounces.
So since 132 ounces would be a bit more than the 128 ounces it would mean it would take 10–2/3 12 oz cups to make 1 gallon of liquid.
That would be 128 ounces of liquid which is 1 gallon.
Then it would take 16 of 8 ounce glasses to make 1 gallon or 128 ounces.