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Scope 3: Your Customer's Spreadsheet Is Your Problem

The questionnaire arrives from your biggest customer: "Please provide your Scope 1, 2 and 3 emissions for the last financial year." Your company has never counted a kilogram of carbon. The questionnaire has a deadline.

Scope 3 is where small businesses meet climate reporting, usually unwillingly. Here's what it is, why it keeps landing in your inbox, and how to answer it without hiring a consultant.

The three scopes in one minute

Scope 1 is what you burn and emit directly: company vehicles, gas boilers, refrigerants, your own factory processes. Scope 2 is the electricity and heat you buy. Scope 3 is everything else — the emissions that happen in someone else's operation but count against your product's total. The GHG Protocol divides it into 15 categories, from purchased goods and upstream transport to business travel and the use of your sold products.

The trick nobody tells small suppliers: your customer's Scope 3 includes your Scope 1 and 2, plus your upstream supply chain. When a big retailer reports "Scope 3, category 1: purchased goods", they're aggregating data that only their suppliers can provide. You are the data source. That's why the questionnaire keeps arriving.

Which categories actually matter for you

Don't memorise 15 categories. For a small manufacturer, three cover almost everything a customer asks:

  • Category 1 — purchased goods. The raw materials and components you buy. Usually your biggest category by far.
  • Category 4 — upstream transport. Getting those goods to you.
  • Category 11 — use of sold products. For energy-using products, the electricity your product consumes over its life. Often the largest category for appliances and tools.

If you're a service business, category 6 (business travel) and category 7 (employee commuting) join the list. That's it. Answer well on those and you've answered 90% of every questionnaire.

How to calculate without losing your mind

The order of operations:

  1. Scope 1 and 2 first. Fuel, electricity, refrigerants. Bills and meter readings, one spreadsheet, an afternoon. These are the numbers with the least uncertainty.
  2. Category 1 with spend-based estimates. Multiply what you spend per material category by an emissions factor from a database built for exactly this. It's an estimate, not a measurement, but it's the accepted starting point for small firms — the GHG Protocol itself expects suppliers to start spend-based and improve.
  3. Upgrade the big lines only. One material might be 70% of your purchased goods. Ask that supplier for their data first. Hybrid models — supplier data for the big lines, spend-based for the rest — are standard practice.

If this sounds familiar, it's the same logic as the product carbon footprint work we described in the ISO 14067 guide. Company-level Scope 3 and product-level footprints share the same underlying data; collect it once.

What good answers look like

Buyers don't expect a small supplier to have audit-grade Scope 3. They expect: a number with a base year, a note on methodology ("spend-based, category 1 and 4 only"), and a trend line next year. "We don't track this" loses the questionnaire; "here's our honest estimate and how we'll improve it" passes it.

The frameworks agree on this shape — CDP's supplier questionnaire, EcoVadis evidence, CSRD value chain requests all want the same numbers in slightly different clothes. We covered the corporate reporting side in the CSRD guide and the software question in the ESG tools buyer's guide. The data you build for one serves them all.

Make the number public

One more thing, and it saves more time than the calculation itself: publish the result. A live, dated company-level page with your scopes, methodology and base year means the next customer questionnaire gets answered with a link instead of a project — one page serving every customer at once. That's the model Sustalium works on — €10 per document, one URL that stays current when your numbers change. Scope 3 is never finished, after all. Make it a page that updates, and you'll only ever do this work once.

How Sustalium Helps with Scope 3

  • One company-level page — scopes, methodology and base year on a single URL every customer questionnaire can link to.
  • Update once a year — new numbers replace old ones everywhere at once.
  • Same data, more frameworks — the inventory behind your Scope 3 answers also feeds CDP, EcoVadis and CSRD value chain requests.

Answer Every Questionnaire with One Link

Publish your scopes once and let every customer self-serve the data. Start structuring your data free and publish the verified asset when you are ready.

Start Your Carbon Accounting →

Frequently Asked Questions

Which Scope 3 categories matter for a small manufacturer?

Category 1 (purchased goods), category 4 (upstream transport) and category 11 (use of sold products) cover almost everything customers ask about.

Is spend-based data acceptable?

Yes, as a starting point. The GHG Protocol itself expects suppliers to start spend-based and improve. Hybrid models — supplier data for the big lines, spend-based for the rest — are standard practice.

Do I need software?

No. For a small firm, a spreadsheet plus a public page gets you to the same answer. The bottleneck is data collection, not formatting.

Last updated: September 20, 2026

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