Every product and service leaves a trail: raw materials extracted, energy consumed, emissions released, and waste generated, from the first stage of production to the moment it is disposed of. Life Cycle Assessment (LCA) is the internationally standardised method, defined in ISO 14040 and ISO 14044, for quantifying that entire trail so decisions can be based on evidence rather than assumption.
This introduction covers what a functional unit is, the four phases of an LCA, the difference between primary and secondary data, the tools and databases practitioners use, and the practical questions a well built LCA can answer.
What is a Functional Unit?
A functional unit is the quantified performance of a product system, used as the reference basis to which all inputs and outputs are related. It is the single most important choice in an LCA, because it defines what is actually being compared.
Rather than comparing “a plastic bottle” to “a glass bottle”, an LCA compares the function both deliver, for example “packaging and delivering 1 litre of drinking water to a consumer”. This matters because a glass bottle is heavier and may need to be transported differently, or a reusable bottle may need to be washed and reused a certain number of times before it outperforms a single use alternative. Without a clearly defined functional unit, comparisons between products are not meaningful.
The Four Phases of an LCA
ISO 14040 structures every LCA into four iterative phases.
Goal & Scope Definition
Defines the functional unit, system boundaries, allocation approach, and intended use of the study.
Life Cycle Inventory (LCI)
Collects all inputs and outputs, materials, energy, emissions, and waste, across every stage of the life cycle.
Life Cycle Impact Assessment (LCIA)
Translates inventory data into environmental impact categories such as climate change, water use, and land use.
Interpretation
Identifies significant findings, checks completeness and consistency, and draws conclusions and recommendations.
Primary vs Secondary Data
Primary data is collected directly from the specific process or supplier being studied, for example metered electricity consumption at a factory, or a supplier’s own measured emissions. It is the most accurate and representative data available, but it is also the most time consuming and expensive to collect.
Secondary data comes from external databases, literature, or industry averages, used to fill gaps where primary data is unavailable or disproportionately costly to collect, for example the average emissions of producing steel or generating grid electricity in a given country. Most real world LCAs blend both: primary data for the foreground processes that matter most to the result, and secondary data for background processes further up the supply chain.
Popular LCA Software Tools
| Tool | Notes |
|---|---|
| SimaPro | One of the most widely used commercial LCA tools, known for its depth of impact assessment methods and database integration. |
| openLCA | A free, open source LCA tool that supports multiple databases and is popular for its flexibility and lower cost of entry. |
| Sphera (GaBi) | An enterprise grade LCA and sustainability platform, widely used for corporate and product level assessments. |
| Brightway | An open source, Python based LCA framework favoured by researchers and practitioners who want scriptable, reproducible, and highly customisable models. |
Process-Based vs Input-Output Databases
Process based databases, such as ecoinvent, build up a product system from individually modelled processes (a specific furnace, a specific transport route, a specific energy mix), giving detailed, technology specific results, though every process only extends so far up the supply chain before data runs out (the “truncation” problem).
Input-output (IO) based databases, such as EXIOBASE, are built from national economic input-output tables, capturing the entire economy, including every upstream supplier, at the cost of lower resolution, since data is typically averaged at the level of an economic sector rather than a specific product. Many practitioners use hybrid models that combine detailed process data for what matters most with input-output data to capture the remaining, harder to trace, upstream supply chain.
What Questions Can an LCA Answer?
A well scoped LCA is a decision making tool, not just a reporting exercise. Common questions include:
How ecorune Can Help
We build LCAs that are scoped to answer a real business question, using the data, tools, and databases appropriate to your product, sector, and budget, from a first screening study through to a fully verified, standards aligned assessment.