A Customer Asked for Our Carbon Footprint. What Do We Actually Send Them?

The email lands on a Tuesday. One of your biggest customers — or a procurement team you've never spoken to — wants your carbon footprint. Scope 1, 2 and 3. Possibly a questionnaire link. Possibly a deadline.

You've never produced a carbon footprint in your life.

If that's where you are, this guide is the short version of what to do. The good news, and it's genuinely good: the amount you actually need to send is far less than you fear, and most of the data is already sitting in your accounts.

First: why you're being asked

You almost certainly aren't in scope of any carbon reporting regulation. Your customer probably is — or is under pressure from their customers, investors or lenders.

Here's the mechanic that catches suppliers out: your emissions are your customer's Scope 3. A large company can't report its own supply-chain emissions without data from the businesses it buys from. So the request travels down the chain until it reaches you.

This isn't a passing fashion. Large organisations across every sector now run structured supplier engagement programmes, and lenders increasingly factor emissions data into credit decisions. If it's your first request, it won't be your last. For the full picture of which UK regulations are driving these requests, see our guide to what UK SRS and SECR mean for small suppliers.

The thing nobody tells you: there's a cap on what they can demand

This is the single most useful fact in this article, and most suppliers don't know it.

Under the EU's Omnibus package (in force since March 2026), there is now a legal limit on how much sustainability data a large CSRD-reporting company can demand from a smaller supplier. That limit is a standard called VSME — the voluntary standard for SMEs, published by EFRAG.

The relevant part for a first request is the VSME Basic Module: around 51 data points, in which Scope 1 and Scope 2 are required and Scope 3 is optional. Almost all of it comes from records you already hold.

So when the request arrives and it looks enormous — you're allowed to answer proportionately. A customer cannot compel a small supplier to produce a full corporate-grade inventory. Knowing that changes the whole shape of your response.

(If you're a UK supplier to a UK customer, VSME isn't law for you — but it's fast becoming the reference point for what a reasonable supplier request looks like, and it's a perfectly good yardstick to aim at.)

What they actually want

Strip away the formatting, and almost every supplier carbon request is asking for the same handful of things:

1. Your Scope 1 and 2 emissions, in tonnes of CO₂e (tCO₂e), for a stated reporting year. This is the core of it — the gas and fuel you burn, and the electricity you buy. If you're new to what Scope 1, 2 and 3 actually mean, that link is the quick explainer.

2. Scope 3, if you have it. Often optional on a first request, increasingly asked for. An estimate is acceptable, as long as you say it's an estimate and explain your method.

3. Your method. Which emission factors you used (in the UK, DEFRA/DESNZ), which standard (the GHG Protocol), and which reporting year. A number with no methodology behind it is worth very little to them.

4. What you're doing about it. Do you have a reduction target? A net zero commitment? Some questionnaires ask, some don't.

The format varies — a spreadsheet from their procurement team, a portal like EcoVadis, CDP or Sedex, or a simple email. The underlying question is the same in all of them.

How to answer, step by step

Step 1 — Ask what they actually need. Before you do anything, ask which reporting year they want, which scopes, and by when. Ask whether an estimate is acceptable for Scope 3 (usually yes). Five minutes of clarification saves you days of work in the wrong direction.

Step 2 — Pull your Scope 1 and 2. Gas and fuel bills, fleet mileage, electricity kWh. Multiply by the current DEFRA/DESNZ factors. This is the part most businesses can do quickly — and it's what your customer most wants.

Step 3 — Estimate Scope 3 from your spend. You cannot survey every supplier you've ever paid, and you don't need to. The recognised route for a first estimate is the spend-based method — your spend by category, multiplied by published emission factors. It's an approximation, you label it as one, and it's a legitimate answer. (We explain the method in full in how to calculate Scope 3 from spend data.)

Step 4 — Send a short, clear summary. Not a sustainability report. One or two pages: your company name, the reporting year, headcount or turnover for context, your Scope 1, 2 and (estimated) 3 figures in tCO₂e, the method and factor set you used, and any reduction commitment. That's it.

Step 5 — Be transparent about gaps. Say plainly what's estimated and what's measured. A partial, clearly-labelled answer beats a late one, and it beats a confident one that falls apart under a follow-up question.

The mistakes that cost suppliers

Ignoring it. The single worst option. Silence gets you flagged as a risk in your customer's supply chain and, over time, quietly replaced by a supplier who answers.

Over-building. Spending six weeks and a consultant's fee producing an audit-grade inventory for a request that needed a two-page summary. Match the effort to the ask.

Inventing numbers. Increasingly, customers apply quality gates — they check the methodology, and they don't accept everything they're sent. A defensible estimate with a stated method is worth far more than an impressive figure you can't explain.

Treating it as one-off. Reporting is annual. The customer who asked this year will ask again next year, and others will join them. If your answer lives in a spreadsheet somebody built once and left, you'll do the whole thing again from scratch.

And it's about to get sharper in the public sector

If you supply the NHS or bid for government contracts, the bar is rising. On 9 June 2026, NHS England published new NHS Carbon Reduction Plan requirements, replacing the current guidance from 1 April 2027: suppliers bidding for NHS contracts of £5m a year or more will need to report Scope 1, 2 and all relevant Scope 3 categories under the GHG Protocol, with a board-approved Carbon Reduction Plan. That's the most demanding supplier carbon requirement in UK procurement — and it's coming.

If a public-sector tender is on your horizon, start with our PPN 006 Carbon Reduction Plan guide.

Answer it once, properly

The reason this feels so painful the first time is that most businesses go looking for the data from scratch — chasing bills, building spreadsheets, hunting for emission factors.

But the raw material is already in your accounting system. You've been categorising your spend for years.

SpendToScope connects to Xero, QuickBooks or Sage and turns that data into a Scope 1, 2 and 3 footprint — with the methodology and factor set stated, in a format you can send straight to a customer. And because it refreshes as your invoices sync, next year's request takes minutes rather than starting over.

The bottom line

• You're being asked because your emissions are your customer's Scope 3 — not because you're breaking any rule.
• Under Omnibus, VSME caps what a large customer can demand: Basic module, ~51 data points, Scope 1 and 2 required, Scope 3 optional.
• What they want is a short summary: tCO₂e by scope, the reporting year, your method — not a corporate report.
• Estimate Scope 3 from spend, label it as an estimate, and move on.
• Answer proportionately, answer honestly, and set it up so next year's request is a five-minute job.