A 5-minute guide to conducting a Life Cycle Assessment (LCA)- Step 2 Inventory analysis (LCI)

Once the Goal & Scope of the LCA is defined (Step 1), the next step is to quantify all the inputs and outputs of the product system across its life cycle.

In Step 2, we collect data on:

• Energy & material inputs
• Emissions, waste, and resource use outputs

This phase results in the Life Cycle Inventory (LCI).

The outcome is not yet environmental impact, it is a structured dataset of flows that will later be translated into impact categories in Step 3 (LCIA).

What is Life Cycle Inventory (LCI)?

LCI is a data-collection and modeling process:

To support this process, most LCA practitioners using LCI databases, which contain datasets describing thousands of real-world industrial activities such as:

• textile production
• electricity generation
• chemical processing
• transport operations
• waste treatment
• recycling processes

These datasets include elementary flows, meaning exchanges between the technosphere and the environment (e.g., CO₂ emitted to air, water consumed from nature).

Examples of LCI databases commonly used:

• ecoinvent
• GaBi / Sphera
• Agribalyse
• USLCI

They provide background data for processes that are difficult to measure directly.

👕 Example: LCI Modeling for a T-Shirt

Let’s continue with the white cotton T-shirt example from Step 1.

To build the LCI model, we follow three key actions:

1) Gather the “Activity Data”

Activity data describes how much of each process is required to produce the functional unit.

Examples:

• mass of materials (cotton fibre, buttons, labels)
• factory energy use
• transport distances
• washing frequency during use phase

For example:

To produce one T-shirt, we need 0.25 kg of cotton fibre.

This data usually comes from:

• company production data (primary data)
• literature and reports
• engineering assumptions
• industrial averages

These values form the reference flows of the model.

2) Match Activity Data with LCI Datasets

Next, we link the activity data to relevant datasets in the LCI database.

Example:

A suitable dataset in ecoinvent may be:

“market for fibre, cotton”

The dataset unit is 1 kg of cotton fibre.

If our T-shirt requires 0.5 kg of cotton, then:

The LCI dataset is multiplied by 0.5 to reflect the quantity needed for the functional unit.

This step ensures that:

• our model reflects real-world production conditions
• the same dataset can be reused consistently
• system modeling remains transparent and reproducible

This process is often called life cycle modeling.

3) Define the Baseline Scenario

The baseline scenario must be consistent with:

• functional unit
• system boundary
• intended use of results

For example:

Scope: cradle-to-grave (raw materials → manufacturing → distribution → use → end-of-life)

For each life-cycle stage, we:

• identify processes involved
• assign relevant LCI datasets
• quantify flows based on activity data

Examples of inventory elements for the T-shirt in ecoinvent:

This baseline becomes the reference case against which future scenarios (eco-design, material change, recycling) can be compared.

Output — What Do We Get?

The result of LCI analysis is:

• a complete process network model
• quantified material & energy flows
• emissions and waste output per functional unit

Typical LCI outputs include:

• kg CO₂ emitted
• MJ of energy used
• m³ of water consumed
• kg of solid waste generated

Here, the goal in step 2 LCI data model is to ensure:

• data completeness
• consistency with scope
• transparency of assumptions

A LCI model example of a T-shirt:

Accroding to the internal BOM(Bill of material) of a T-shirt, find a proxy or the closed match in the LCI database, take ecoinvent as an example: here is the BOM and the possible proxy in ecoinvent:

and since in ecoinvent, the database “market for fibre, cotton…” and “market for printed paper”… do not included the raw material acqusition, therefore, in here need to model also the raw material and the transportation, use phase, and end-of-life of the product.

Congrats you have made it here! step 2 is the very important part in LCA, next chapter will talk about the step 3 Life Cycle Impact Assessment (LCIA), translate flows into impact categories (e.g., climate change, water use, land use…).