Your Customer Just Asked for Your Scope 3 Data. What Now?

You received an email from a customer asking for your company's carbon emissions data. Possibly they attached a form, a spreadsheet, or a link to an online portal. It may have mentioned Scope 3, Category 1, GHG Protocol, or CSRD. If none of that means anything to you yet, you're not alone — and this is not a request you should ignore.

Here's what's happening, why it matters, and what you actually need to do.

Why Are You Getting This Request?

Your customer is building a greenhouse gas emissions inventory. Under frameworks like the GHG Protocol, they are required to account for the emissions embedded in everything they purchase — that's Scope 3 Category 1, Purchased Goods and Services. You, as a supplier, sit inside that category.

The three most common reasons customers send these requests:

• CSRD compliance. The EU Corporate Sustainability Reporting Directive requires in-scope companies to disclose Scope 3 emissions. Large EU companies have been subject to this since January 2025, with broader application rolling out over subsequent years. Their auditors expect documented Scope 3 inventories.
• Science Based Targets (SBTi). Companies that have committed to SBTi near-term targets are typically required to engage their top suppliers on emissions data, and in some cases to set supply chain targets.
• Procurement requirements. An increasing number of large buyers are embedding emissions disclosure into their procurement process — not as a nicety, but as a condition for remaining on the supplier list.

In short: this is a growing and formalising obligation. Responding well positions you as a preferred supplier; not responding at all can cost you the relationship.

What Does Your Customer Actually Need?

Most of these requests are asking for one or more of the following:

• Your total spend as a supplier to their organisation, by category — so they can apply an emission factor themselves using the spend-based method.
• Your own emissions data — specifically your Scope 1 and Scope 2 emissions, which they can use as a more accurate input than a sector average.
• A product- or service-level emission factor — the emissions per unit of what you sell. This is primary data and requires more work, but gives the buyer the most accurate calculation.
• Methodology disclosure — how you calculated any figures you provide, which emission factors you used, and what standard or database they came from.

Many buyers are not expecting perfect primary data from every supplier. They are looking for a credible, documented response they can present to their own auditors.

Spend-Based Estimates vs Primary Data

There are two fundamentally different things you could provide, and it helps to understand the difference.

Spend-based estimate

A spend-based estimate takes the amount your customer paid you, multiplied by an emission factor for your sector from an EEIO database such as EXIOBASE or the EPA's supply chain factors. Your customer may already have done this calculation themselves — what they might be asking for is confirmation that the spend categorisation is correct.

Spend-based estimates are fast to produce and acceptable under GHG Protocol as secondary data. Their limitation is that they reflect the average emissions intensity of your sector, not your specific operations. A supplier with a clean energy mix gets the same factor as one running coal-heavy processes.

Primary data

Primary data means actual emissions figures from your own operations — your own Scope 1 and Scope 2 inventory — or a product-level lifecycle assessment (LCA). This is higher quality under GHG Protocol data quality tiers, but requires that you have already done your own emissions accounting.

If you have a carbon inventory already, sharing your Scope 1 and 2 totals per product category is a reasonable response. If you don't, a well-documented spend-based estimate is the appropriate starting point — and is what most buyers at this stage will accept.

For a deeper look at what Category 1 inventories contain and how they're built, see our post on Scope 3 Category 1 explained.

What a GHG Protocol Category 1 Inventory Looks Like

If you're being asked to produce or provide a Category 1 emissions inventory, here's what that document typically contains:

• A list of suppliers or spend categories
• The spend amount per supplier or category, in a consistent currency
• The EEIO sector each spend line was classified into
• The emission factor applied (in kgCO₂e per unit of spend), and its source
• The resulting emissions estimate per line
• A total in kgCO₂e (or tCO₂e)
• A methodology note explaining the approach

The document needs to be traceable. If an auditor asks the buyer to justify a particular line item, the buyer needs to be able to point to the source invoice and the classification logic that produced the emission estimate. A summary table without lineage will not survive a third-party assurance review.

Practical Steps to Respond

If you've received a Scope 3 data request and don't have a carbon accounting platform, here's a workable approach:

1. Identify what you actually sold this customer. Pull your invoices to them for the relevant period (usually the calendar or financial year they specify). These are your source documents.
2. Categorise the spend. For each product or service category, determine which EEIO sector it maps to. If you sell a range of products, you may need to split the spend across categories.
3. Apply emission factors. Use publicly available EEIO data — the EPA USEEIO or EXIOBASE datasets are commonly referenced and freely available. Match your spend categories to sectors in the database and apply the relevant factor.
4. Document everything. Record the methodology, the factors used, their version and source, and keep a link back to the source invoices. This is what makes a response audit-ready rather than just a number in an email.
5. Respond in writing. Share the inventory with a short methodology note. If the customer provided a specific format or portal, use that.

The whole process can be done from existing invoices without specialist software — but the classification and documentation steps are where most of the time goes. Tools like ZeroDocPro can automate the extraction and classification step from your invoice PDFs directly.