Wondering whether that “eco-friendly” product is really better for the planet? A life cycle assessment measures a product’s environmental impact from raw materials to disposal, following four ISO 14040 phases, so you can compare options fairly.
If you want the wider context first, read what is sustainability and then see how individual products get measured.
| Key fact | Value |
|---|---|
| Framework standards | ISO 14040 and ISO 14044 |
| Number of phases | Four, iterative |
| Default scope | Cradle to grave |
| Product carbon footprint standard | ISO 14067 |
| Environmental Product Declaration standard | ISO 14025 |
| Climate factor for methane | 29.8 (100-year GWP), in kg CO₂-eq |
These figures come from GreenSutra’s life cycle assessment guide and Decerna’s step-by-step guide. Standards, methods and factors can change, so check the sources before you rely on them.
What a life cycle assessment measures
A life cycle assessment, often shortened to LCA, evaluates the environmental impact of a product, process or service across its entire life cycle. That runs from raw material extraction and processing through manufacture, distribution, use and final disposal.
Unlike a single number, an LCA looks at many impact categories at once. The result shows not only the carbon footprint but also the demands placed on water, land and finite resources.
The evidence a study produces supports four kinds of decision:
- Finding the environmental hotspots that drive cost and impact.
- Informing decisions on materials, design and process.
- Preparing an organisation for regulatory and procurement requirements.
- Supporting claims that customers, investors and regulators can verify.
The four phases of a life cycle assessment
Every study follows the ISO 14040 principles and the ISO 14044 requirements. The four phases run in order yet stay iterative, because interpretation can send the study back to refine the goal, the inventory or the boundary.
- Goal and scope definition. You set the purpose of the study, the functional unit and the system boundary.
- Life cycle inventory (LCI). This collects input and output data for every process in the system, and it typically consumes most project time and resources.
- Life cycle impact assessment (LCIA). This converts the inventory of emissions and resources into environmental impacts.
- Interpretation. This analyses results, checks reliability and draws conclusions.
Reporting is an ISO 14044 requirement rather than an official fifth phase. The same standard also calls for a critical review where a public comparative assertion is made.
The first phase matters more than it looks. A 2017 chapter in the EPA HERO database notes that its importance is often underestimated, because the goal and scope are defined at the outset, before any data are collected. They can still be modified as new information appears, but such changes should be described transparently in the final report.
Choosing the functional unit and system boundary
The functional unit creates the reference point for the whole study. It must be measurable and relevant to how products actually get used, so you compare the function a product provides rather than “one product”.
Typical examples show how this works:
- Packaging: containing 1 litre of beverage for 30 days.
- Transport: moving one person 10 kilometres.
- Buildings: providing 100 m² of usable floor space for 50 years.
Packaging is a common case for these comparisons, and the guide on sustainable packaging puts the material choices in context.
The system boundary decides which life cycle stages the study covers. The two most common approaches sit at opposite ends of the same axis:
- Cradle to grave covers the full life cycle, from raw material extraction through manufacture, distribution and use to end of life disposal.
- Cradle to gate stops at the factory gate, before distribution and use, capturing the upfront, embodied impact.
- Three further approaches cover circular, single-stage and fuel cases: cradle to cradle, gate to gate and well to wheel.
Any exclusions should be documented. If a study cuts off processes contributing less than 1% of mass or energy, it should state that cut-off criterion clearly. The data matter too: primary data comes from direct measurement, while secondary data comes from databases.
How impacts are calculated and compared
Once the inventory is complete, LCA software applies characterisation factors. Each emission or resource use is multiplied by its impact factor and summed within categories.
Standard sets of impact categories include:
- Climate change
- Ozone depletion
- Acidification
- Eutrophication
- Human toxicity and ecotoxicity
- Water scarcity
- Resource depletion
- Land use
The climate category shows the logic. CO₂ gets a factor of 1, methane gets 29.8 on a 100-year basis, and nitrous oxide gets 273. Summing these gives a total climate change impact in kg CO₂-eq.
The choice of assessment method, such as ReCiPe, CML, TRACI or Environmental Footprint, affects results, particularly for toxicity categories. That is why the method should be documented and justified.
Two optional steps come after that. Normalisation compares results to reference values such as average per capita impacts. Weighting combines categories into a single score, but it involves value judgements and shouldn’t be used for publicly disclosed comparative assessments without clear justification.
How LCA differs from a carbon footprint and an EPD
People often use three terms as if they meant the same thing. They are related, but they are not interchangeable:
- A full life cycle assessment is the broadest study.
- A product carbon footprint under ISO 14067 is the single climate indicator inside it.
- An Environmental Product Declaration under ISO 14025 is the third party verified declaration of the results, with EN 15804 applying to construction products.
The wider view has a practical benefit. Because the carbon footprint sits inside the assessment, a design choice that lowers carbon but raises water use stays visible rather than hidden.
What can go wrong, and how to read a result?
A study is only as strong as its weakest input. Three weak points deserve attention before you trust a result:
- Data gaps. Missing data for significant processes weakens results, so gaps should be identified early and addressed.
- Allocation choices. When a process generates several products, ISO 14044 favours avoiding allocation through subdivision or system expansion. If that is unavoidable, allocation follows physical relationships such as mass or energy content, with economic allocation used when physical relationships don’t apply.
- Weighting. Collapsing many categories into one score hides value judgements.
These weak points are why scope and review matter when a claim goes public. A claim resting on one stage or one indicator is the kind of thing that what is greenwashing warns about, so a clear boundary and a critical review add credibility.
When you meet an LCA-backed claim, a short checklist helps:
- Is the functional unit stated, and does it match how you would use the product?
- Does the boundary cover the stages that matter, such as raw materials or the use phase?
- Does the study look beyond carbon to other impact categories?
- Was a critical review carried out for any public comparison?
Frequently asked questions
What does LCA stand for?
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LCA stands for life cycle assessment, a method that evaluates the environmental impact of a product, process or service from raw material extraction through disposal.
What is the difference between cradle to grave and cradle to gate?
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Cradle to grave covers the full life cycle through end of life disposal. Cradle to gate stops at the factory gate, before distribution and use.
Is a carbon footprint the same as a life cycle assessment?
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No. A product carbon footprint under ISO 14067 is the single climate indicator inside a wider assessment, which also covers categories such as water use.
Can the goal and scope change during a study?
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Yes. They are defined before any data are collected, but they can be modified as new information is revealed. Such changes should be described transparently in the final report.
