A functional unit is the reference unit used in a Life Cycle Assessment to measure and compare environmental impacts. It defines how much of a product or service you are assessing — and makes it possible to compare different products on a meaningful, like-for-like basis.
Without a functional unit, comparing the footprint of a small glass bottle with a large plastic container would be meaningless. The functional unit provides the common basis.
Examples of functional units
Product | Possible functional unit |
T-shirt | 1 garment |
Bottled water | 1 litre of drinking water delivered to consumer |
Packaging | 1 unit of product packaged and protected |
Laptop battery | 1 kWh of energy delivered over product lifetime |
Paint | 1 m² of surface covered with 10 years durability |
The key is that the functional unit captures the purpose of the product — not just its physical form.
How Root uses functional units
In Root, environmental impacts are calculated and expressed per product unit as defined in your product portfolio. When you upload a Bill of Materials for a product, the material weights are recorded per unit of that product — this becomes the functional unit for all impact calculations.
This means:
Product impacts in your dashboards are always shown per unit (e.g. kg CO2e per T-shirt)
When scaled by sales volumes, Root can aggregate impacts across your entire portfolio
Comparing two products side-by-side in Root is meaningful as long as they share the same functional unit
Functional unit vs declared unit
In formal LCA reporting and Environmental Product Declarations (EPDs), a distinction is sometimes made between:
Functional unit: The unit based on the function the product performs (e.g. 1,000 washes of laundry)
Declared unit: A simpler physical quantity used when the full function is hard to measure (e.g. 1 kg of detergent)
Root uses declared units — product units as defined in your system — which is standard practice for product portfolio LCA at scale.
FAQ
What if my products come in different sizes?
If your products differ in size or weight (e.g. S, M, L), each should ideally have its own BOM reflecting the actual material quantities for that size. If this is impractical, you can use the proxy feature to apply one product's BOM to similar variants, with a weight adjustment factor.
Does changing the functional unit change the total company footprint?
No. The total company footprint is calculated by multiplying per-unit impacts by sales volumes. Changing how you define a unit affects per-unit comparisons, but the aggregate company footprint is driven by actual production quantities.