In LCA, there are two types of units of measure; the functional unit and the declared unit.
A functional unit is a quantitative description of the function of a product system that enables a fair and meaningful comparison between alternative products or services.
The functional unit should be chosen to reflect the main function of the product or service being studied.
A declared unit, on the other hand, is a unit of measure used to report the results of an LCA. It is a standardized way of expressing the functional unit and enables comparisons between different product systems. The declared unit may be the same as the functional unit or may be different, depending on the requirements of the study.
For example, if the functional unit is "one liter of milk produced," the declared unit might be "the environmental impact per liter of milk produced." This allows for meaningful comparisons between different milk production systems, regardless of their size or other factors.
Pickler calculates the environmental impact (eco-costs) per piece of the finished packaging as a declared unit. Therefore, the functional unit is 'one piece of packaging'.
In some cases, the functional unit needs to be adapted. For example, if the packaging is made to order per square meter or when the weight of one piece is unknown. The alternative then is to compare per 1kg of the finished packaging material.
The eco-score (A,B,C,D,E,F,G) is determined based on a functional unit of 1 kg packaging material. The reason for this was to eliminate the difference between different sizes of the same type of packaging.