Scope 3 for suppliers: what your customer is asking for and where to start

Why the request reached you

Scope 3 is the Greenhouse Gas Protocol (GHG Protocol) term for all the indirect emissions in a company's value chain. The GHG Protocol Scope 3 Standard splits them into 15 categories, from the goods a company buys to the use and disposal of what it sells.

Your own Scope 1 and 2, the fuel you burn and the electricity you buy, sit inside your customer's Scope 3 under purchased goods and services. When your customer measures its supply chain, it needs your figures to do it.

For large buyers, that supply chain is usually the biggest part of the footprint. CDP's Scope 3 Upstream report, written with Boston Consulting Group and published in June 2024, found that companies reporting to CDP put their supply chain emissions at 26 times their operational emissions (Scope 1 and 2) on average.

Targets add pressure. Under the Science Based Targets initiative (SBTi) near-term criteria, a company whose Scope 3 is 40% or more of its total emissions must set a Scope 3 target. Its Scope 3 targets must cover at least 67% of those emissions. Reaching that coverage almost always means involving suppliers.

What your customer's target means for you

The SBTi's supply chain guidance describes three ways a company can set a Scope 3 target. Each one lands on you differently.

A supplier engagement target commits your customer to having a set share of its suppliers, by emissions or by spend, set science-based targets of their own. The SBTi's guidance says it must be met within five years of the target being submitted. Your customer is working to a fixed deadline and will track whether you move.

Customers often rank suppliers by their share of Scope 3 and include the largest until they reach the coverage they need. If you are a smaller supplier you may still be asked for data, because your customer needs it for its own calculations.

What the request usually contains

Requests come as questionnaires, supplier portals, third-party data platforms or plain emails. The content is similar whichever route it takes:

• your total Scope 1 and 2 emissions for a recent year, with the method and factors used;
• your Scope 3, at least screened, with the largest categories estimated;
• the share of your emissions allocated to that customer, often by revenue or quantity;
• carbon footprints for the products they buy most, where you have them;
• whether you have a reduction target and what you are doing to meet it;
• whether any of your figures have been independently checked.

Start with your own Scope 1 and 2

You do not need to finish everything before you reply. Your customer mainly wants to see steady progress, and the first thing it needs is your own baseline.

Build Scope 1 and 2 for your most recent full year from fuel and electricity records, with the factor and source for each line. Our guide to measuring a small manufacturer's footprint walks through it step by step.

Then work out the share for this customer. Revenue is a common basis: if the customer takes a fifth of your sales, a fifth of your emissions is a reasonable first allocation. Say which basis you used, so the customer can compare like with like.

Then screen your own Scope 3

Go through all 15 categories and note which apply. For most manufacturers, purchased goods such as metals, polymers, chemicals and packaging are likely to be the largest. If your products use energy, such as motors or pumps, the use of those products can matter too.

Use spend data from your purchase ledger for a first, complete picture: money spent multiplied by a factor per pound for that type of purchase. It is quick but relies on broad averages. Improve the largest lines over time with quantities and then with figures from your own suppliers, as set out in our guide to collecting emissions data from suppliers.

Report what you did. Say which categories you include, which you exclude and why, and which figures are estimates.

How to reply well

• Answer on time, even if only in part.
• Mark estimates as estimates, and say when you expect to improve them.
• Answer every customer from the same records, so your numbers stay consistent.
• Keep the method the same as in your own reporting.
• Name one contact for follow-up questions.
• Say what you are doing to cut emissions, as well as what they are.

If you are asked to set a target, you have options. The SBTi has a route for smaller companies and a standard route; check the current eligibility rules before you choose. Where a validated target is not yet realistic, a public commitment backed by a measured baseline shows movement. Ask your customer whether it counts towards its programme. More on science-based targets.

How ESGen helps suppliers answer

The ESGen platform builds your Scope 1 and 2 from electricity, gas, diesel and petrol, using the DESNZ factors for the right year. It also adds staff car mileage and the upstream energy share of Scope 3. Every figure keeps its bill, factor and calculation, so a follow-up question has an answer.

Our team prepares questionnaire answers that match your reported figures. Scope 3 beyond energy, carbon per product and the data behind a science-based target submission are new pieces of work that we scope with you first. The SBTi validates targets, not ESGen. See how this fits your supply chain work.

If a customer request is sitting in your inbox, book a demo and bring it with you.