Identifying the Functional Unit if there are different comparing sizes

Question

Hi, I would like to comapre the LCA results of an 1 litre PET bottle with a 0,4 litre glass bottle (for the same kind of lemonade).

How should I choose the functional unit if the bottles have different sizes? Can I choose 1 litre of lemonade as the functional unit and then multiplicate the LCA results of the 0,4 litre glass bottle by the factor 2,5 to get the results for 1 litre?

Answer 1

Well the question is if you can at all compare then the different sizes. Do they provide the same benefit? If you think yes then fine, but it seems a bit questionable.