A normalisation factor is a factor applied to an amount of an Impact category indicator to express the amount relative to a normalisation reference. This transformation step in Life Cycle Impact Assessment helps to contextualise impact assessment results by comparing them to a reference situation.
Normalisation is an optional element within the Life Cycle Impact Assessment phase, as outlined in ISO 14044. The process involves dividing the characterised impact results by a corresponding normalisation reference value. This conversion allows practitioners to express environmental impacts in relative terms rather than absolute values, making it easier to understand the magnitude and significance of impacts in context.
The normalisation factor itself is calculated by taking the reciprocal of the normalisation reference amount. When this factor is multiplied by the characterised impact result for a given impact category, the outcome represents the proportion of that impact relative to the chosen reference scenario. For example, if a normalisation reference represents the total annual impact for a specific geographical area, applying the normalisation factor reveals what fraction of that total annual impact is attributable to the product system under study.
Common normalisation references include per capita annual impacts for a specific region (such as Europe or globally), sectoral impacts, or impacts from total economic activity within a defined geographical boundary. The choice of normalisation reference significantly influences the interpretation of results, as different references provide different perspectives on the relative significance of impacts.
By applying normalisation factors across multiple impact categories, it becomes possible to identify which environmental impacts are relatively more significant for a given product system. This facilitates comparison across diverse impact categories that otherwise use different units and scales, supporting more informed decision-making in sustainability assessment.
