No, you will have to compare the individual products yourself. But since products of the same type is usually on display close to each other, and the price is displayed in the same unit, it's not very hard. In practice, this means that most products have two prices listed - first, the actual price of the product, second the "comparison price", per standard unit. For example:

Brand A, Orange Juice, 1L. 19.90 (Price per Litre: 19.90) Brand B, Orange Juice, 2L. 30.00 (Price per Litre: 15.00)

This is simply to spare the consumer of doing the math themselves, which can turn out to be quite tricky in some cases (although not in my example:)