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Scope 3 for suppliers: what your customers want from your emissions data
Your customer's Scope 3 includes your emissions. When a large buyer asks for supplier emissions data, it wants your Scope 1 and 2 footprint, the share that belongs to it, and a credible plan to cut it, so it can replace estimates in its own report with real numbers.
Why is my customer asking for our emissions data?
Because your emissions are part of theirs. Under the GHG Protocol, everything a company buys counts towards its Scope 3, and purchased goods and services is usually the biggest category. CDP found that supply chain emissions are on average 11.4 times a company's own operational emissions. When your customer reports its footprint or sets a target, most of that number is you and suppliers like you.
Targets make it sharper. The Science Based Targets initiative requires a Scope 3 target when Scope 3 is more than 40% of a company's total emissions, and that target has to cover at least 67% of Scope 3. Many large buyers meet it with a supplier engagement target: a set share of their suppliers, by spend or emissions, with science-based targets of their own. If you're one of their big suppliers, you're inside that percentage.
If you don't send a number, your customer estimates one from what it spends with you. That estimate only moves when the invoice moves, so nothing you do to cut emissions will ever show up in their report.
What does a supplier emissions data request ask for?
The wording changes from customer to customer. The questions underneath rarely do.
| They ask for | What it means | What you need |
|---|---|---|
| Your carbon footprint | Scope 1 (fuel you burn) and Scope 2 (electricity you buy) for the last full year | 12 months of energy and fuel records |
| Their share | The part of your footprint caused by what you make or do for them | A fair allocation method, written down |
| Your own Scope 3 | The emissions in your supply chain, at least for the main categories | Spend data by category, then supplier data for the big ones |
| Targets | A public commitment to reduce, ideally validated | A baseline year and a target that covers the right scopes |
| A product footprint | Emissions per unit of a specific product, from raw materials to your gate | Bill of materials, process energy and transport data |
Most mid-sized suppliers get the first two requests first. Product footprints tend to come later, and mostly in manufacturing, food and consumer goods.
How do you report carbon emissions as a supplier?
- Measure Scope 1 and 2. Use 12 months of fuel and electricity data and the UK Government's greenhouse gas conversion factors. This is the number almost every request asks for first.
- Screen your Scope 3. A first pass using spend by category shows which purchases matter. Expect a handful of categories to dominate.
- Split it by customer. Allocate your footprint by revenue, mass, units or machine hours, whichever reflects how your work is really used. State the method, because customers will compare it year to year.
- Set a target and a plan. A dated baseline, a reduction target and the actions behind it. Customers increasingly score the plan as well as the number.
- Answer from one dataset. CDP, EcoVadis, a customer portal or a spreadsheet: point them all at the same numbers and update them once a year.
What is the difference between spend-based and supplier-specific data?
The GHG Protocol gives four ways to calculate the emissions from purchased goods. The spend-based method multiplies what was spent by an industry-average factor. The average-data method uses mass or quantities instead. The hybrid method mixes a supplier's own activity data with averages, and the supplier-specific method uses the supplier's actual product-level data.
Spend-based is quick and crude. Supplier-specific is what your customer wants from you, because it is the only kind that reflects your efficiency, your energy and your materials. A supplier that can provide it moves from being a guess in someone else's report to being a known, measurable part of it.
What does the NHS net zero supplier roadmap need from April 2027?
From 1 April 2027, the next step of the NHS Net Zero Supplier Roadmap takes effect. NHS England's new Carbon Reduction Plan rules apply to procurements for contracts worth £5 million a year or more, including VAT, and to all new frameworks and dynamic markets where proportionate. The plan must cover Scope 1, Scope 2 and all relevant Scope 3 categories, with any category left out explained. It must use a global boundary, include targets that have been independently validated and be approved by the board or a director, then published on your website.
Smaller contracts keep the 2024 format: Scope 1 and 2, plus five Scope 3 categories (upstream transport and distribution, waste from operations, business travel, employee commuting, and downstream transport and distribution). That is a much bigger jump than it looks. Our page on Carbon Reduction Plans and SBTi covers both formats.
What this could earn you. Measuring for a customer puts your energy, freight and materials costs side by side, often for the first time. That is usually where the waste shows. A credible number also delivers competitive advantage in tenders where rivals can only send estimates.
The supplier who answers first, with a real number, sets the standard the others are judged against.
Common questions
Do suppliers have to report Scope 3 emissions?
Not by UK law, for most. Streamlined Energy and Carbon Reporting (SECR) asks large UK companies to report energy use and Scope 1 and 2 emissions, and leaves Scope 3 voluntary. The pressure comes from customers, and from 1 April 2027 the NHS asks suppliers on contracts of £5 million a year or more for all relevant Scope 3 categories.
What is a supplier carbon footprint?
The total greenhouse gas emissions a supplier's business causes in a year, measured as Scope 1, Scope 2 and usually Scope 3. Customers use it, or the share allocated to them, in their own Scope 3 reporting.
How do you work out a customer's share of your emissions?
Divide your footprint using a measure that reflects how your work is used: revenue, mass, units or machine hours. Revenue is the simplest and physical measures are more accurate. Use the same method each year and tell the customer which one you used.
Is spend-based Scope 3 data good enough?
For a first screen, yes. It can't show reductions you make, because it only changes when spend changes, so customers with targets will push for supplier-specific data over time.
Need a number you can defend? See our Scope 3 consultant service and fixed fees, or read how to build a Scope 3 reduction strategy.