I make my own ice cream using 1/2 pint whipping cream, eggs, sugar and flavourings and it fills 3/4 of an empty litre cannister. Why doesn't your son contact an ice cream manufacturer (somewhere local, not Walls) and ask them? I think that's the only place he'd get the type of answer that he needs. But I do think that as you have to add content to milk/cream/what have you/ then you will end up with more volume for the end result so it has to be more than a litre I would have thought.