A customer has asked for carbon data. The email may say "carbon footprint", "GHG data", "Scope 3", or name a GHG Protocol category. You supply products or services, not climate accounting, and you need to know what they want.
The short version: a number for the emissions associated with what you sell them, with a note on how you got it. Before you calculate anything, establish which of the following they are asking for.
| First question | Short answer |
|---|---|
| Whose emissions do they want? | Yours. Your Scope 1 and 2 (and your own Scope 3 if you have it) become one line in their Scope 3. |
| Company-level or product-level? | Ask. Most first requests accept a company-level figure allocated by revenue or volume. Product-level is more work. |
| What if I have never calculated emissions? | Send activity data — kWh, liters, cubic meters, material quantities — with a note. Their team can apply factors. |
| What format? | Whatever they sent. If nothing, a one-page table: period, boundary, sources, factors, numbers, gaps. |
| What happens if I send nothing? | They estimate from what they paid you, using industry averages. That usually overstates your footprint. |
Why customers are asking now
The EU's Corporate Sustainability Reporting Directive requires large companies to report their full greenhouse gas emissions, including Scope 3 — everything in their value chain they do not directly control. That includes their suppliers.
After the 2026 Omnibus changes, CSRD applies to companies with more than 1,000 employees and €450 million turnover. Those already reporting continue; the rest start with financial year 2027. Their suppliers are being asked for data now because the customer needs a baseline before the first mandatory report, and large buyers pass the request down regardless of whether the supplier has any reporting obligation of its own.
Expect the request to become annual.
Whose scope is it
One paragraph on vocabulary. The GHG Protocol sorts a company's emissions into three scopes. Scope 1 is what it burns itself: fuel in boilers, furnaces, and vehicles, plus refrigerant leaks. Scope 2 is the electricity, heat, or steam it buys. Scope 3 is everything else in its value chain, including the emissions of its suppliers.
Your Scope 1 and 2 (and your own Scope 3, if you have it) are what your customer records as their Scope 3. When they ask for your carbon footprint, they want the figure that becomes one line in their supply-chain total. You are not being asked to calculate their emissions. Only yours.
The 15 Scope 3 categories and where you fit
The GHG Protocol defines 15 categories of Scope 3 emissions, upstream and downstream. Four matter for suppliers.
Category 1: purchased goods and services. Where you appear in your customer's report. The emissions from producing and delivering what you sell them land here. For most suppliers this is the only category that matters.
Category 2: capital goods. If you sell equipment, machinery, or other capital assets, your products fall here instead.
Category 4: upstream transportation. If you arrange transport of goods to the customer, those logistics emissions may be relevant.
Category 9: downstream transportation. If the customer arranges transport, those emissions are their Category 9 and not your concern.
The other categories — business travel, commuting, waste, leased assets, investments — are the customer's own operations. They do not need them from you.
What they need, ranked
Total emissions in metric tons CO2e
The ideal: one number for the total greenhouse gas emissions associated with what you supplied, in metric tons of carbon dioxide equivalent, with a documented methodology.
Calculating it means multiplying activity data by emission factors. If you have not done this before, the carbon footprint calculation guide for manufacturers covers the method, and the free carbon calculator does the multiplication from your energy and fuel figures.
Activity data
If you cannot calculate emissions, send the inputs and let the customer's sustainability team apply the factors:
- Electricity consumption in kWh, with your country or grid region
- Natural gas in kWh or cubic meters
- Fuel in liters (diesel, petrol, LPG)
- Material inputs by weight (metric tons of steel, plastic, chemicals)
- Production volumes (units produced, metric tons shipped)
- Water in cubic meters
- Waste in metric tons, by disposal route
This is the practical minimum. Customers with mature programs have tools that convert activity data into emissions with standard factors. Clean activity data is useful without a final CO2e figure. The energy consumption tracking guide covers gathering the energy part.
Emission factors and methodology
When you do calculate, document which factors you used and where they came from:
- The factor source (DEFRA, IPCC, national grid publications)
- The year the factors apply to
- Location-based or market-based accounting for electricity
- What is inside and outside the calculation boundary
- Assumptions and estimates
A number without methodology is difficult for an auditor to accept. A documented estimate is more useful than an undocumented figure that looks precise.
Product-level or organization-level
Some customers want the emissions of the specific product they buy from you. Others accept an organization-level figure allocated by revenue or volume. Ask which.
Product-level data — a product carbon footprint, or PCF — needs the energy, materials, and processes behind one item. It is more work and more accurate for their Category 1. The product carbon footprint guide covers it.
Organization-level data divided by revenue share is simpler: if a customer is 15% of your revenue, they take 15% of your total. A reasonable starting point when product-level data does not exist.
The data quality hierarchy
Reporting frameworks rank supplier data in a clear order.
Supplier-specific data. Your actual emissions from your real energy, fuel, and material inputs. What they want.
Average data. Industry averages or product-category factors applied to quantities purchased. Acceptable; less accurate.
Spend-based estimates. What they paid you multiplied by an average emissions-per-euro factor for your industry. Least accurate, and what they use when you send nothing.
When you provide no data, the customer does not leave a blank. They estimate from spend, and spend-based averages are dragged up by the least efficient producers in the sector. Real data usually makes your footprint look better than the default. Providing it is in your interest, not only theirs.
What format they want
Their template. Many companies send a supplier data collection spreadsheet. Fill it in as sent. Do not substitute your own format.
CDP Supply Chain. Large multinationals often route Scope 3 collection through CDP. The CDP supply chain guide covers it.
EcoVadis. Some customers use the EcoVadis environment section as a proxy for supplier carbon data.
Procurement platforms. SAP Ariba, IntegrityNext, Ecodesk, and similar have supplier sustainability modules; you may be asked to enter data directly.
A plain spreadsheet. Smaller customers, or those early in their Scope 3 work, accept a clean spreadsheet with documented data.
Whatever they sent, respond in that format. Ease of processing matters almost as much as the data.
Presenting your numbers
When no template is provided, a complete response has seven parts: the reporting period; the organizational boundary (all sites, or only the site supplying this customer); the emission sources covered and anything excluded; the methodology and emission factors; the numbers; a data quality note (measured versus estimated, known gaps); and what will improve next time.
A table carries most of it:
| Category | Emissions (tCO2e) | Notes |
|---|---|---|
| Scope 1 | 45.2 | Natural gas + fleet diesel; DEFRA 2025 factors |
| Scope 2 (location-based) | 112.8 | Purchased electricity, 480,000 kWh, national grid factor |
| Total | 158.0 | Calendar year 2025, all sites, operational control |
Customers reviewing dozens of supplier responses need exactly this: scannable, methodology visible, gaps stated.
Intensity metrics. Many customers also want the footprint normalized for size: per unit of production (kg CO2e per unit), per revenue (tCO2e per €1 million), or per employee (tCO2e per FTE). If they do not specify, provide the absolute figures and one relevant intensity metric. If you are growing, the absolute number can rise while intensity improves; report both.
Common mistakes
Percentages without absolute numbers. "We reduced emissions 10%" says nothing without the base. They need metric tons.
Confusing whose scope is whose. Your Scope 2 is your purchased electricity. It lands in their Scope 3. Report yours; let them place it.
Outdated emission factors. Grid electricity gets cleaner most years. A 2018 factor applied to 2025 consumption overstates your footprint. Use the factor for the reporting year.
Over-engineering. A one-page table with a methodology note beats a fifty-page report that buries the number.
Ignoring their format. If they sent a template, fill in the template.
If you have never tracked emissions
The deadline is close and there is no inventory. What you can supply this week:
- Twelve months of electricity bills. Sum the kWh. Note your country.
- Twelve months of gas bills. Sum the kWh or cubic meters.
- Fuel. Liters of diesel or petrol for company vehicles and equipment, from fuel cards or receipts.
- Major materials purchased. Metric tons of key inputs (metals, plastics, chemicals, packaging).
- Production volume. Units produced or metric tons shipped to this customer.
- Gaps, stated. What is estimated, what is missing, what you plan to improve.
Send this as activity data with a note that formal emissions calculation is in development. It is more than most suppliers provide. To plan the work against the deadline, the free time estimator gives a figure based on what you already have.
Improving each year
Scope 3 data quality is expected to improve, not to be complete at once.
Year 1. Activity data. Energy bills, fuel records, material quantities. The customer applies their own factors.
Year 2. Calculated emissions. You apply recognized factors (DEFRA, national databases) to the activity data and report in metric tons CO2e, with methodology documented.
Year 3. Refined. Product-level footprints where feasible. Third-party verification for key figures. Year-on-year comparison.
No customer expects year 3 in the first response. They expect the direction.
Why responding matters commercially
Procurement teams managing hundreds of suppliers record who responds and who does not. Between two suppliers with comparable products and prices, the one who provides documented carbon data on time makes the customer's reporting easier; the one who ignores the request creates a compliance gap someone has to chase.
You do not need the lowest footprint in your sector. You need a credible, documented, timely response. Most suppliers are not yet providing one.