Scope 3 of the GHG Protocol: the 15 categories, data and methods

Scope 3 of the GHG Protocol groups the indirect emissions of the value chain into 15 categories: 8 upstream, tied to what the company buys, and 7 downstream, tied to what it sells. Each one needs a different data point, from a different source, with a different calculation method. That is where the real difficulty lies.

According to Scope 3 Upstream: Big Challenges, Simple Remedies, published by Boston Consulting Group and CDP in June 2024 with 2023 data, the supply chain emissions of reporting companies are on average 26 times higher than their operational Scope 1 and 2 emissions. Only 15% of those companies have a Scope 3 reduction target.

What is Scope 3 and why is it so hard to calculate?

Scope 3 covers the greenhouse gas emissions a company does not directly control but which are generated as a consequence of its activity: purchasing, transport, use of sold products, waste treatment and investments. Scopes 1 and 2 are calculated from your own invoices; Scope 3 depends on third parties who do not always hold the data or have any duty to hand it over.

Pressure comes from two directions. The CSRD, after Directive (EU) 2026/470 published on 26 February 2026, keeps Scope 3 as central reporting content where it is material, even though scope has narrowed to companies with more than 1,000 employees and 450 million euros in turnover, with financial year 2027 as the first reporting year. Separately, large customers ask for it contractually long before any legal obligation arrives.

If you are starting from zero, our guide to starting your Scope 3 emissions journey covers the first steps.

What are the 15 categories and what data does each need?

This table is the operational part: what you have to obtain, where it usually sits and which GHG Protocol method turns it into emissions.

How do you decide which categories to calculate?

The GHG Protocol does not require you to calculate all fifteen. It requires you to assess all of them and justify any exclusions. The standard sets six relevance criteria:

1. Size. The category contributes a significant share of total emissions.
2. Influence. The company can act on it.
3. Risk. It is linked to climate, regulatory or reputational risk.
4. Stakeholders. Customers, investors or suppliers consider it critical.
5. Outsourcing. It covers activities that used to be in-house.
6. Sector guidance. The sector identifies it as significant.

The practical route is a hotspot analysis first, using spend factors across the whole procurement ledger, then finding where 80% of the impact sits, and refining only those categories with primary data. Document the analysis: that is what a verifier will ask for before accepting an exclusion.

How do you keep data quality defensible?

The hierarchy is always the same, best to worst:

• Primary supplier data, with a calculated and ideally verified product footprint.
• Material or process-specific factors from a recognised database.
• Average data by mass or physical unit, when you know the quantity but not the origin.
• Spend factors, useful for screening but blind to any supplier improvement.

Three practices make an inventory survive an audit: declaring what share of each category was calculated with each data type, documenting uncertainty rather than hiding it, and setting an annual target for replacing estimates with primary data. If the bottleneck is getting that data, how to overcome the supplier data barrier explains how to structure the campaign.

Is the Scope 3 Standard about to change?

Yes, it is under revision. On 31 March 2026 the GHG Protocol published a Phase 1 progress update on the revision of the Corporate Value Chain (Scope 3) standard. These are draft proposals, pending public consultation and approval by the Independent Standards Board, but they signal the direction:

• A 95% coverage threshold of required Scope 3 emissions, with a 5% exclusion allowance.
• A new Category 16 for other value chain activities, including facilitated emissions, with insurance and underwriting moving out of Category 15.
• Disaggregation by data type and a disclosure of whether Scope 3 is fully, partially or not verified.
• Data specificity goals with metrics such as the percentage of primary data.

None of this is enforceable yet. The sensible move is to start tagging the origin of every data point now, because it is the most likely requirement and the most expensive one to retrofit.

How to reduce Scope 3 once you have calculated it

1. Concentrate the effort. In most companies, twenty suppliers explain the bulk of category 1.
2. Put the data in the contract. Footprint reporting clauses and progressive improvement targets work better than one-off requests.
3. Handle transport with shared frameworks. The GLEC Framework and ISO 14083 let you compare operators and ask them all for the same data format.
4. Redesign the product. Categories 11 and 12 are tackled at the design table, not in procurement.
5. Align targets across the chain. Science-based targets give suppliers and customers a common language.

If you want to understand how climate risk propagates along the chain, we have an analysis of the impact of climate change on the supply chain.

Frequently asked questions about Scope 3

Is Scope 3 reporting mandatory in Spain?

For companies in CSRD scope, yes where it is material. Royal Decree 214/2025 does not require it from the private sector: it mandates Scope 1 and 2 and leaves Scope 3 voluntary. In the MITECO carbon footprint registry it is also voluntary, although registering it triggers mandatory external verification.

Where do I start with no supplier data?

With last year's procurement ledger. Spend per category plus spend factors produces a hotspot map in a few days, enough to know who to ask for primary data.

Which categories weigh most by sector?

In automotive and appliances, use of sold products, category 11, dominates. In food, fashion and retail, category 1 rules. In banking and insurance, category 15. In professional services, categories 6 and 7.

Can spend-based estimates be used?

Yes, the GHG Protocol accepts them, but they have a serious management flaw: if a supplier decarbonises without changing its price, the estimate does not move. They are for screening, not for tracking progress.

How do you justify excluding a category?

By documenting the relevance analysis against the standard's six criteria and roughly quantifying what is excluded. An exclusion with no number behind it rarely passes verification.

What is the difference between the GHG Protocol and ISO 14064-1 on Scope 3?

ISO 14064-1:2018 organises indirect emissions into categories that differ from the GHG Protocol's fifteen, although the content overlaps. We compare them in GHG Protocol versus ISO 14064-1.

To maintain a Scope 3 inventory with the audit trail a verifier expects, and to automate reading supplier invoices and documents, you can rely on Manglai's carbon footprint platform and its artificial intelligence features.