lol. Anywhos, There are 28 empty 12 ounce cans in a pound per the recycling station up the road. There are 16 ounces in a pound. Divide 16 by 28 and you get .5714285 ounces per empty can.
It depends on a number of factors but roughly speaking beer weighs a fraction more than water, in metric units about 1050Kg per cubic metre. To convert that into pounds per cubic feet divide by 16.02...