Declared unit

The declared unit is what one footprint describes, such as one T-shirt, one pair of shoes or one kilogram of fabric.

Two footprints can only be read side by side if they use the same unit. A per-kilogram figure and a per-item figure describe different things, even for the same product.

Where a footprint compares products that do the same job, the term functional unit is used instead, describing that job, such as one year of wearing a garment.