The main reference is the GHG Protocol Corporate Value Chain (Scope 3) Standard and its Technical Guidance for Calculating Scope 3 Emissions. For target setting you typically align with the Science Based Targets initiative (SBTi), which builds on GHG Protocol data and defines how much and how fast emissions need to fall when setting targets in line with limiting global warming to 1,5 °C.

Yes. In addition to the core GHG Protocol and SBTi guidance, many sectors now have specific standards or handbooks:

• SBTi sector guidance: e.g. for chemicals, steel, power, transport and FLAG (land‑use‑related) sectors.
• Industry associations: often publish sector‑specific guidance, relevant emission factor or LCA data, and best practices.

Using sector guidance helps you align with peer practice and makes the results of your calculations easier to compare.

You first define your organisational boundary for your calculation, then apply it consistently to Scope 1, 2 and 3. Take the following steps:

• Decide on the consolidation approach, either financial control (include entities you control financially), operational control (include entities where you control day‑to‑day operations), or equity share (include emissions in proportion to your ownership share). Ensure consistency in the consolidation approach chosen for GHG emissions (scope 1,2,3) as well as financial reporting for the organisation.
• Apply this to all subsidiaries, joint ventures, branches, and significant leased assets.
• Make sure the same boundary is used for Scope 3 category calculations where relevant (e.g. outsourced activities, contract manufacturing, etc.).

You include Scope 3 categories that are relevant (material) to your business. The GHG Protocol suggests looking at:

• Size: expected share of total emissions (hotspots).
• Spending or revenue: high‑spend or high‑revenue areas can have high emissions.
• Influence: where you can realistically reduce emissions based on control or leverage.
• Risk and stakeholders: categories important for clients, investors, regulators and NGOs.
• Sector practice: what peers and sector guidance consider standard.

You should document why each category is included or excluded and review this regularly as your business or data changes.

Start from the 15 categories and, for each relevant category, identify:

• Activity volumes: physical quantities such as tonnes purchased, kilometres transported, kWh used, number of products sold.
• Financial data: spend per supplier, category or project where physical data is missing.
• Emission factors: per unit of activity or spend, from databases, suppliers, LCAs or industry sources. Ecomatters has extensive experience with and access to various sources for emission factors to cover this data need.
• Context data: supplier names, locations, modes of transport, contract types, etc., to allow better future refinement.

Prioritise high‑impact categories and use data sources that are auditable and repeatable. Using a well-designed template for this process makes (annual) data collection, audits, and future handovers easier.

No. The level of detail should be proportional to the relevance of each category. For categories with higher relevance, you’ll need more detailed, activity-based data. For categories with lower relevance, it’s acceptable to use less granular approaches, such as spend-based estimates or secondary data, as long as the approach is transparent and representative. For some categories, specific rules on the use of activity-based or spend-based data are provided by the Technical Guidance for Calculating Scope 3 Emissions. You should document your decisions and the rationale behind them.

Activity data: concrete measures of an activity in the respective unit.

• Examples: kWh of electricity, kilometres travelled, tonnes of steel purchased, number of laptops bought.

Spend data: monetary value used as a proxy.

• Examples: € spent on freight, € spent on raw materials, € spent on business travel.

Activity data is usually more accurate because it is directly linked to the physical process, while spend data is useful when quantities are unknown or too hard to obtain. Check out this article if you want to know more.

Yes. For most categories, the preferred order is:

1. Specific activity data: Activity data measured directly from the source (e.g., metered supplier emissions data, actual fuel use, direct monitoring), and uses specific emission factors tied to the actual activity.
2. Non-specific / average activity data: Secondary data that is averaged or representative of a group of similar activities (e.g., industry average emissions per unit). May use generic emission factors.
3. Spend-based data: spend-based proxies where value or spending is used with spend-based emission factors.

You can mix methods across categories, and even within a category, as long as you are transparent and focus the best data on the biggest emission sources.

The template should be set up per category to capture the specifics of each category. For example, when collecting specific activity data this consists of the following:

• Category and activity description: e.g. Category 1 – purchased steel.
• Required activity data: e.g. tonnes of material, km per mode, kWh, units sold.
• Preferred units: tonnes, km, MWh, pieces, €.
• Emission factors and source: database name, version, supplier LCA, etc.
• Data owner in the organisation: e.g. procurement, HR, logistics, etc.
• Update frequency: yearly, quarterly, per project.

Conducting Scope 3 calculation requires GHG emission inventory input data from across the organisation. Examples include:

• Procurement: supplier data, contracts, spend and sourcing strategy.
• Logistics  and operations: transport, warehousing, packaging, process data.
• HR: commuting, business travel, headcount, office locations.
• Sales department: product portfolio, customer segments, use‑phase insights.
• Finance  and control: spend data, consolidation boundary, investments.
• IT / Data management: systems for obtaining, storing, and automating data where relevant.

It is not strictly required by the GHG Protocol, but strongly recommended for key categories and hotspots:

• It increases accuracy compared with using secondary data such as from databases.
• It allows better tracking of reduction measures and lower‑carbon products.
• It improves alignment with SBTi expectations

A tiered approach works well: focus supplier engagement on the suppliers that drive most of your emissions (by spend, volume or hotspot analysis) and use generic data for the rest.

These downstream activities are covered by Category 10 (Processing of sold products) and Category 11 (Use of sold products). Common approaches are to Scope 3 GHG emission inventory development are:

• Build scenarios and assumptions: product lifetime, typical use patterns, energy consumption, and disposal routes.
• Combine internal expertise with customer input and sector studies or statistics to refine these assumptions.
• Use (secondary) market or LCA data when detailed customer data is not available and clearly document boundaries and limitations.

For products with many diverse end‑uses, you may focus on the most material applications and explain where robust quantification is not yet feasible.

Good documentation is essential for transparency, audits and year‑on‑year consistency.

You should:

• Record organisational boundaries, category relevance assessments, and reasons for inclusion/exclusion.
• Describe methods and data sources per category (data sources, emission factors, assumptions).
• Keep version‑controlled files so you can see how methodologies change over time.
• Note any baseline recalculations and indicate whether changes are due to better data, application, or updated emission factors.

This information can sit in a methodology document that underpins your annual sustainability report.

Most companies update Scope 3 calculations annually, aligned with their financial and sustainability reporting cycles. You should also consider:

• Making quarterly data updates to regularly changing categories such as energy, logistics or major raw materials to track deviations early. This is especially relevant if you have set targets.
• Conducting a baseline recalculation when structural changes occur (e.g. mergers, divestments, major methodology or emission‑factor updates, or changes > ~5% of base‑year emissions).

• Re‑evaluating categories when your business model or organisational boundary changes (new product lines, new regions, new joint ventures).

If you want to have deeper understanding of multi-annual Scope 3 GHG emissions inventory development you can read more about it in this whitepaper.