---
title: "A customer asks for your carbon data:\nhow do you prepare a reliable reply?"
description: "Carbon footprint assessment, product footprint, CDP or EcoVadis: what a customer can demand from a supplier, the Omnibus cap and the file to prepare once."
canonical: https://projetcelsius.com/en/blog/customer-carbon-data-request/
author: "Guillaume Pakula"
datePublished: 2026-10-17
dateModified: 2026-10-17
language: en
translationOf: https://projetcelsius.com/blog/client-demande-donnees-carbone-reponse/
---

# A customer asks for your carbon data: how do you prepare a reliable reply?

**Author**: Guillaume Pakula
**Published**: 2026-10-17
**Section**: Practical guide
**Canonical URL**: https://projetcelsius.com/en/blog/customer-carbon-data-request/
**French original**: https://projetcelsius.com/blog/client-demande-donnees-carbone-reponse/
**Source**: Projet Celsius (https://projetcelsius.com/en/), a climate strategy consultancy of engineers and PhDs based in Paris and Marseille.

> A supplier can prepare the reply to a customer asking for its carbon data itself, **provided it knows which data is expected**: the company's assessment, a product footprint or the emissions of a delivery. No law requires a reply, except for transport, and for its sustainability statement a customer will be able to demand on climate from a supplier with **no more than 1,000 employees** only its energy and its Scope 1 and 2 emissions. A file prepared once then serves **every questionnaire**.

## Key takeaways

- A request for carbon data targets **a company assessment, a product or a delivery**.
- Only the carbon data of a transport service is **required by law**.
- On climate, the Omnibus cap is limited to **energy and Scopes 1 and 2**.
- Send **your consumption figures and your allocation key**, not a single figure on its own.

A single request for "carbon data" can mean 3 very different things: the company's carbon footprint assessment, the footprint of a product or the emissions of a delivery. The [CDP supply chain programme](https://www.cdp.net/en/supply-chain) alone approached **more than 45,000 suppliers** in 2025, and each customer words its question in its own way. The work therefore starts by **translating the request** into one of these 3 kinds of data.

A supplier that has prepared these 3 kinds of data once can then answer most questionnaires **without starting again**, whether the request comes from a manufacturer, a retailer or a [public buyer](https://projetcelsius.com/en/blog/public-procurement-environmental-criterion-how-to-respond/).

## What data does the customer ask for?

Behind the wording used by procurement teams, "your carbon footprint", "your footprint", "your emissions", the data expected almost always falls into one of **3 families**. Telling them apart from the outset avoids producing a full assessment when the customer wanted the footprint of a single product reference, or the reverse.

### The company's carbon footprint assessment

This is the most frequent request: the **company's emissions** over a year, **Scope 1** for its fuels and vehicles, **Scope 2** for purchased electricity, sometimes Scope 3 for its purchases and transport. They are calculated under the Greenhouse Gas (GHG) Protocol or the Bilan Carbone® method (the French carbon accounting method), whose differences our [comparison](https://projetcelsius.com/en/blog/bilan-carbone-vs-ghg-protocol/) sets out. The [voluntary standard](https://eur-lex.europa.eu/eli/reg_del/2026/1560/oj) published in the Official Journal of the European Union on 21 September 2026 adds **energy consumption** in megawatt hours (MWh). The customer that receives this assessment must then **allocate** it to isolate the share that relates to it, and it is often up to the supplier to give it the key.

### The footprint of a product

A customer calculating its own Scope 3 prefers the footprint of the product it buys, **from cradle to factory gate**, because it adds directly to its quantities. It is calculated under ISO 14067 or the [PACT methodology](https://www.carbon-transparency.org/resources/pact-methodology-v3), through an approach close to a [life cycle assessment (LCA)](https://projetcelsius.com/en/blog/product-carbon-footprint-lca-pef-cfp/) that the company's own assessment **does not replace**. For a construction product, this data already exists in the form of a [verified FDES](https://projetcelsius.com/en/blog/fdes-pep-choose-accredited-verifier/), the French format of environmental product declaration for construction products.

### The emissions of a service

For a carrier, the data is required by law in France. [Article L1431-3 of the French Transport Code](https://www.legifrance.gouv.fr/codes/article_lc/LEGIARTI000031066016) requires anyone who organises a transport service to inform its customer of the **quantity of greenhouse gases** emitted. Since 1 January 2025, failure to do so is punishable by a fine of up to **€3,000**. The calculation uses **default values**, company-specific averages or measurements per service, set out in our article on [a carrier's carbon footprint assessment](https://projetcelsius.com/en/blog/road-haulage-carbon-footprint/).

## Is a supplier required to reply?

Outside transport, **no law requires** a supplier to give its carbon data to a customer. The constraint is **commercial or contractual**, and European law now limits what a large customer can demand of a medium-sized supplier.

### The contract and the call for tenders

A **contract clause** or a tender criterion creates the obligation, at least to win the contract, and a customer that [assesses its suppliers with EcoVadis](https://projetcelsius.com/en/blog/does-ecovadis-replace-a-carbon-footprint/) often makes it a condition for being listed as a supplier. In public procurement, [Article 35 of France's Climate and Resilience Act](https://www.legifrance.gouv.fr/jorf/article_jo/JORFARTI000043957012) requires **at least one** award criterion to address the environmental characteristics of the bid, for procedures launched since 22 August 2026. Our guide to [responding to the environmental criterion](https://projetcelsius.com/en/blog/public-procurement-environmental-criterion-how-to-respond/) sets out how to score points.

### The value chain cap set by the Omnibus Directive

The [Omnibus Directive of 24 February 2026](https://eur-lex.europa.eu/eli/dir/2026/470/oj) protects companies with **no more than 1,000 employees**. When a customer subject to the [Corporate Sustainability Reporting Directive (CSRD)](https://projetcelsius.com/en/blog/csrd-2026-who-is-in-scope-after-omnibus/) asks them for information for its sustainability statement, they may refuse anything that goes beyond the voluntary standard, and **no contrary clause** in a contract is binding on them. The customer must **inform them** of this, and it may rely on their self-declaration of size.

On climate, this cap is narrow. Annex II of the voluntary standard includes, for a company with more than 10 employees, only **energy consumption** and **gross Scope 1 and 2 emissions**, with Scope 2 calculated using the local grid. It includes no climate data for a company with 10 employees or fewer. The cap applies to financial years beginning **from 1 January 2027**, and the directive must be transposed by 19 March 2027 at the latest.

Scope 3 and the product footprint therefore remain **outside the cap**, which does not make them enforceable for the sustainability statement. A request made for other reasons, a tender or a procurement strategy, is not covered by this right of refusal, as our article on the [revised ESRS](https://projetcelsius.com/en/blog/revised-esrs-2026/) points out. Our article on [whether Scope 3 is mandatory](https://projetcelsius.com/en/blog/is-scope-3-reporting-mandatory/) sets out this rule and its limits.

## Who can prepare the reply?

The reply does **not always need a consultancy**. What decides is the data expected and the use the customer will make of it, as with the choice between [software](https://projetcelsius.com/en/blog/carbon-accounting-software-vs-consultancy/) and [a consultancy](https://projetcelsius.com/en/blog/carbon-footprint-consultancy-how-to-choose/) for a full carbon footprint assessment.

### In-house, for Scopes 1 and 2

Scopes 1 and 2 are calculated from energy bills, fuel logs and refrigerant top-ups, using public emission factors. A team that keeps these figures can **do it itself**, within the limits described in our article on [doing your own carbon footprint assessment](https://projetcelsius.com/en/blog/do-your-own-bilan-carbone-cost/), and say so frankly in its reply. Errors of unit, year or forgotten emission category are frequent, and our list of the [pitfalls of a first carbon footprint assessment](https://projetcelsius.com/en/blog/first-carbon-footprint-ten-common-pitfalls/) records others.

### With support, for Scope 3 and the product footprint

Scope 3 and the footprint of a product call for **methodological choices** that an informed customer will review: boundary, allocation rule, sources of the factors. Outside support is justified in 4 situations:

- The customer asks for the footprint of a product, which follows a specific standard and is closer to a [first LCA](https://projetcelsius.com/en/blog/first-product-lca-steps-cost-mistakes/) than to a company assessment.
- The customer will use the reply to calculate its own trajectory, and will review it line by line and compare it with those of your competitors.
- The customer requires verification, and the file must then stand up to an independent third party that took no part in the calculation.
- The company has never carried out a full carbon footprint assessment, and the [Diag Décarbon'Action](https://projetcelsius.com/en/blog/diag-decarbonaction-complete-guide/) (a Bpifrance-subsidised carbon footprint programme for companies established in France) can then fund part of the first calculation.

### A third party, when the customer wants verified data

A customer may ask for the data to be verified. For an assessment, this means [verification by a third party (in French)](https://projetcelsius.com/blog/bilan-carbone-interne-verification-tiers/) *(in French)*, often under ISO 14064-3. For [a product footprint exchanged under PACT](https://projetcelsius.com/en/blog/product-carbon-footprint-verification/), the methodology has an independent third party verify **the calculation model** until 2030, rather than each footprint. [EcoVadis](https://ecovadis.com/solutions/ecovadis-carbon-data-reliability-levels/) for its part ranks third-party-verified data **at the top of its 4 levels** of reliability, as the scale below shows.

## How do you prepare a reliable reply?

A reliable reply is one **the customer can review** and reproduce. It is prepared in **4 steps**, from scoping to documentation, and this is what the buyer will check, as our article on [verifying supplier data](https://projetcelsius.com/en/blog/verify-supplier-emissions-data/) describes.

### Have the request clarified

Before calculating, **5 clarifications** prevent a reply that misses the point: the year concerned, the boundary (a site, the company, a product), the **unit expected**, the method required and the use the customer will make of the figure. A customer who wants a footprint per kilogram can do nothing with an annual total in tonnes.

### Start from activity data

The GHG Protocol advises buyers to ask preferably for the data the supplier already holds, such as its **energy consumption**, and to calculate the emissions themselves, which limits errors. The voluntary standard also asks for electricity **as shown on the invoices** of the energy supplier. Passing on the kilowatt hours and litres, with the factors applied, makes the reply **verifiable** by the customer.

### Allocate between customers

A company's assessment is allocated between customers using an allocation key. The [GHG Protocol Scope 3 Standard](https://ghgprotocol.org/sites/default/files/standards/Corporate-Value-Chain-Accounting-Reporing-Standard_041613_2.pdf) asks for the key that best reflects how the emissions are produced. The PACT methodology, following ISO 14067, favours a **physical key**, tonnes, units or volume, and recommends mass in case of doubt. The **economic key**, based on turnover, attributes more emissions to expensive products, as the calculation below shows, built for this article.

The supplier states **the key used** and **the share of its output** bought by the customer. The GHG Protocol also allows it to pass on its total and its share of output, leaving the customer to do the allocation itself.

### Document the method

A reply without a methodology note amounts to an estimate. The note states **the standard followed**, the sources and versions of the emission factors, the exclusions, the year of the data and, for a product footprint, **the share of primary data**, which PACT always has the supplier pass on. It presents separately what is not deducted from a footprint: offsetting, which ISO 14067 places outside its scope, carbon stored in a product and guarantees of origin. A [claimed carbon neutrality](https://projetcelsius.com/en/blog/carbon-neutral-claims-what-companies-can-say/) has no place in the figure.

> A figure the customer can reproduce is worth more than a lower figure it cannot verify.

## What goes into a reusable supplier file?

The **same file** serves the procurement questionnaire, a [first CDP response](https://projetcelsius.com/en/blog/first-cdp-response/), EcoVadis, the voluntary standard and the tender. It consists of a few documents, to be updated every year when the accounts are closed:

- The company's assessment for the latest closed year, Scopes 1 and 2 at a minimum, with energy consumption in megawatt hours and the method followed.
- Scope 3 where it has been calculated, category by category, with the excluded categories and the reason for each exclusion.
- The footprint of the best-selling products, from cradle to factory gate, with their declared unit and the share of primary data.
- The allocation key offered to customers, preferably a physical one, and the table of quantities delivered to each of them over the year.
- The methodology note and, if one exists, the verification statement, with the name of the third party and the level of assurance obtained.

Confidentiality is handled through a **non-disclosure agreement**, or through verification by a third party in place of the detailed activity data, which the GHG Protocol cites as an alternative. The file also serves internally: it prepares the [reduction strategy](https://projetcelsius.com/en/blog/how-to-reduce-company-carbon-footprint/) that customers end up asking for.

There is **no public price list** for this preparation. The cost depends mainly on **what already exists**, a recent assessment or nothing, on [the size of the site](https://projetcelsius.com/en/blog/industrial-site-carbon-footprint/) and on whether a product footprint is requested, whose cost follows that of [an LCA](https://projetcelsius.com/en/blog/lca-cost/). Our [pathway for an SME approached by a customer](https://projetcelsius.com/en/solutions/sme-carbon-footprint/) sets out the steps and the available support. For a full carbon footprint assessment, our article on [the cost of a carbon footprint assessment](https://projetcelsius.com/en/blog/bilan-carbone-cost-france/) and our [simulator](https://projetcelsius.com/en/tools/bilan-carbone-cost-estimator/) give orders of magnitude.

For us, at Projet Celsius, the right reply to a customer is **one it can reproduce** from the data supplied: consumption figures, dated factors, an explained allocation key. A low, opaque figure **costs more** the day the buyer checks it. In [our carbon footprint assessment engagements](https://projetcelsius.com/en/services/carbon-footprint-bilan-carbone/), we build this file once, with the supplier's team, so that it can then answer the questionnaires of the following years on its own.

## Key takeaways

- A request for carbon data targets the company's assessment, a product footprint or the emissions of a service: first find out which.
- Only information on the emissions of a transport service is required by law, with a fine of up to €3,000.
- For its sustainability statement, a customer will be able to demand on climate from a supplier with no more than 1,000 employees only its energy and its Scope 1 and 2 emissions.
- A reliable reply starts from consumption data, allocates the assessment with a physical key and documents its method, without deducting offsetting.
- A file prepared once and updated every year answers most questionnaires, from CDP to public tenders.

To see the same data from the buyer's side, read [how to verify the carbon data of your suppliers](https://projetcelsius.com/en/blog/verify-supplier-emissions-data/), and for the Scope 3 method, [our guide](https://projetcelsius.com/en/blog/scope-3-emissions-guide/).

## Frequently asked questions

### Can a customer require me to provide my carbon footprint assessment?

No law requires it, except French law on information about the emissions of a transport service. A contract or a tender can make it a condition. For its sustainability statement, a customer subject to the CSRD will be able to demand on climate from a supplier with no more than 1,000 employees only its energy consumption and its Scope 1 and 2 emissions, from financial year 2027 onwards.

### What should I reply to a customer asking for my carbon footprint?

First ask the customer to specify whether it wants the company's assessment over a year or the footprint of a product, with the unit, year and method expected. The assessment is calculated from energy consumption and purchases, the product footprint under ISO 14067 or the PACT methodology. In each of the 2 cases, the reply comes with a methodology note.

### How do I allocate my carbon footprint between my customers?

An allocation key is applied to the total. The GHG Protocol asks for the key that best reflects how the emissions are produced, and the PACT methodology favours a physical key, tonnes, units or volume, with mass in case of doubt. The economic key, based on turnover, attributes more emissions to expensive products. The key used must be stated to the customer.

### Does the data sent to a customer have to be verified?

Only if the customer or the framework requires it. EcoVadis places third-party-verified data at the top of its 4 reliability levels, and the PACT methodology has the calculation model for product footprints verified. Verification by a third party can also replace the transmission of confidential activity data.

### Can a customer demand my Scope 3?

Not for its sustainability statement, if the company has no more than 1,000 employees: Scope 3 goes beyond the cap of the voluntary standard, and the company may refuse. The customer may ask for it for other reasons, a contract or a procurement strategy, and otherwise estimates it using averages. Sending its consumption figures and its allocation key lets it make a more accurate calculation.

### How much does it cost to prepare a carbon data reply for a customer?

There is no public price list. The cost depends mainly on what the company already has, a recent assessment or nothing, and on whether a product footprint is requested, which is closer to a life cycle assessment. A file built once and updated every year greatly reduces the cost of later replies.

## Sources

**Sources**: [Directive (EU) 2026/470 of 24 February 2026, amended Article 19a of Directive 2013/34/EU](https://eur-lex.europa.eu/eli/dir/2026/470/oj); [Delegated Regulation (EU) 2026/1560 of 3 July 2026, voluntary standard, Annex I (B3, paragraphs 32, 33 and 49 to 52), Annex II and Article 4](https://eur-lex.europa.eu/eli/reg_del/2026/1560/oj); [Transport Code, Article L1431-3, version in force since 1 January 2025](https://www.legifrance.gouv.fr/codes/article_lc/LEGIARTI000031066016); [Ministry of Ecological Transition, GHG information on transport services](https://www.ecologie.gouv.fr/politiques-publiques/information-ges-prestations-transport); [Law No. 2021-1104 of 22 August 2021, Article 35](https://www.legifrance.gouv.fr/jorf/article_jo/JORFARTI000043957012); [CDP, Supply Chain, accessed 16 October 2026](https://www.cdp.net/en/supply-chain); [EcoVadis, Carbon Data Reliability Levels](https://ecovadis.com/solutions/ecovadis-carbon-data-reliability-levels/); [WBCSD, PACT Methodology, version 3, 30 April 2025](https://www.carbon-transparency.org/resources/pact-methodology-v3); [GHG Protocol, Corporate Value Chain (Scope 3) Standard, 2011, chapters 7 and 8](https://ghgprotocol.org/sites/default/files/standards/Corporate-Value-Chain-Accounting-Reporing-Standard_041613_2.pdf); [ISO 14067:2018, carbon footprint of products](https://www.iso.org/standard/71206.html); cover photo: Romazetti, servo motor packing station in Tula, [Wikimedia Commons](https://commons.wikimedia.org/wiki/File:%D0%AD%D0%BB%D0%B5%D0%BA%D1%82%D1%80%D0%BE%D0%BF%D1%80%D0%B8%D0%B2%D0%BE%D0%B4%D1%8B_%D0%BD%D0%B0_%D1%83%D1%87%D0%B0%D1%81%D1%82%D0%BA%D0%B5_%D1%83%D0%BF%D0%B0%D0%BA%D0%BE%D0%B2%D0%BA%D0%B8.jpg), CC BY-SA 3.0. The Légifrance pages are in French, as is the Ministry of Ecological Transition page.