Responding to a Carbon Data Request From a Key Account Client:
the complete 2025 guide.

Knowing how to respond to a carbon data request from a key account client has become an essential skill for any SME supplier. CSR questionnaire, Scope 3, GHG Protocol, tight deadline — here’s the concrete method to respond without a consultant and in under two hours.

Why your client is asking you this

Since 2024, large European companies have been subject to the CSRD (Corporate Sustainability Reporting Directive). This regulation requires them to measure and publish their carbon emissions, including those of their entire supply chain.

In practice: when Carrefour, Schneider Electric, or Michelin calculates its carbon footprint, it must include the emissions of you, its supplier. Without your data, it cannot complete its own report.

What this means for you: responding is not optional if you want to keep the business relationship. Large groups are starting to prioritize suppliers who can provide this data. Some already make contract renewal conditional on receiving a supplier carbon footprint.

How to respond to a carbon data request from a key account client: what’s really being asked

The questionnaire may seem complex, but in 90% of cases it comes down to measuring three things.

• Scope 1: your direct emissions. Gas or fuel oil to heat your premises, fuel for your fleet, industrial machinery. This is the simplest part to calculate.
• Scope 2: your indirect emissions linked to purchased energy. Mainly your electricity consumption. In France, thanks to the nuclear-heavy energy mix, Scope 2 is generally low.
• Scope 3: everything else. Supplier purchases, transport, employee travel, waste. Often 70 to 90% of the total, but calculable from your accounting expenses.

The good news: you don’t need to calculate Scope 3 with engineering-level precision. The methodologies accepted by clients allow for estimates based on your accounting expenses. Your purchase invoices already contain most of the information you need.

The 4 mistakes to avoid

It won’t go away. It will come back next year, more insistently. In the meantime, your client may have already started sourcing alternatives from suppliers who do respond.

Responsible purchasing teams increasingly check the consistency of the data. A carbon footprint that is obviously underestimated or lacks a methodology can create more problems than no response at all.

A carbon consultant charges between €2,000 and €8,000 for an SME carbon footprint. Justified for certification. Disproportionate for responding to an annual carbon data request from a key account client.

A supplier carbon footprint is not an audit. It’s a methodologically justified estimate. Citing your sources (ADEME Base Carbone, GHG Protocol) is enough to make the report credible in the vast majority of cases.

What you need to respond

Before looking for a tool or a consultant, take stock of what you already have. You probably already have 80% of the information you need in your existing systems.

• Accounting software (Sage, Pennylane, FEC…): your purchases for the year, categorized by item. The basis for the upstream Scope 3 calculation.
• Energy invoices: gas consumption (Scope 1) and electricity consumption (Scope 2) in kWh.
• Fleet or expense reports: kilometers traveled by your vehicles and business trips.
• Lease or floor plans: the surface area of your premises, useful for refining the heating/cooling calculation.

The concrete 5-step method

1. Gather your energy consumption data : Collect your gas and electricity bills for the past 12 months. Record consumption in kWh, not euros. If you have several sites, do it site by site.
2. Export your accounting purchases : From your accounting software, export your expenses for the current year. An Excel export is enough. Important categories: raw materials, supplies, transport, subcontracting.
3. Apply the emission factors : Each expense category corresponds to an emission factor in kgCO₂e. Available for free in the Base Carbone ADEME and in the GHG Protocol guides.
4. Consolidate by Scope : Add up your emissions by Scope 1, 2, and 3 category. The result is expressed in tonnes of CO₂ equivalent (tCO₂e).
5. Write a methodology page : State the sources used (ADEME, GHG Protocol), the reference year, and the confidence level. This page is just as important as the figures — it shows that your assessment is rigorous.

What level of precision to expect

A first supplier carbon footprint will always be an estimate. That’s normal, it’s expected, and it’s acceptable to clients in the vast majority of questionnaires received.

The practical rule: if you cover your Scopes 1 and 2 with measured data, and your upstream Scope 3 with your accounting expenses, you produce a report that satisfies 95% of the supplier questionnaires in circulation.

And next year?

The carbon data request from your key account client will come back every year, with increasing precision requirements. The advantage of having done this work once: the structure is already in place. The following year, it’s no longer about rebuilding everything, but about updating the data. The time required drops from several weeks to a few hours.

This is also the case for investing in a solution that automates data collection and calculation, rather than repeating the manual exercise every year.

Respond to your client’s carbon data request.
In 2 hours. For free.

Oakbon connects to your accounting, applies ADEME emission factors, and generates a Scope 3 report aligned with recognized standards, ready to send to your key account client.

From €69/month · No commitment