Functional Unit

A functional unit is the primary measure of a product or service. ISO states that “the functional unit defines the quantification of the identified functions (performance characteristics) of the product. The primary purpose of a functional unit is to provide a reference to which the inputs and outputs are related. This reference is necessary to ensure comparability of LCA results. The functional unit can be a service, mass of material, or an amount of energy. Selecting appropriate functional units is critical to creating an unbiased analysis. For example, when comparing trains to cars for transportation, the comparison may suffer from the inability to correlate energy inputs and outputs. The real purpose of the train would be to deliver a larger number of people to a specific centralized location. For this example, a better functional unit may be impacts of a train delivering a specific number of people over a specified distance. The results will then be normalized to distance for more reasonable correlations and assessments.