Scope 3 emissions — supply chain mapping and calculation

What are scope 3 emissions?

Scope 3 emissions are the indirect emissions generated throughout an organisation's value chain — everything you don't own or control directly. Where scope 1 covers your direct emissions and scope 2 emissions cover purchased energy, scope 3 captures the upstream and downstream activities that sit either side of your operations: the goods and services you buy, the freight that moves them, the way customers use what you sell, and how it is disposed of at end of life. Together, scope 1, 2 and 3 make up an organisation's full carbon footprint, and most companies find the bulk of it lands in scope 3 — the emissions spread across their value chain rather than inside the factory gate.

For most businesses these indirect emissions are the largest part of the total carbon footprint by a wide margin. That is exactly why scope 3 matters: you cannot set a credible net zero target, or claim real progress on carbon reduction, without first measuring what happens across your supply chain. Scope 3 is where genuine decarbonisation lives, and where the carbon impacts of everyday business decisions really add up.

Scope 3 reporting and credible carbon reporting go hand in hand. An honest emissions assessment of your supply chain emissions gives stakeholders — investors, customers and lenders — confidence that your GHG emissions reflect reality, not a convenient subset of it.

Who this is for

You need scope 3 consultancy if you are preparing for SBTi validation, responding to CDP, answering customer due diligence questionnaires, or want your SECR voluntary scope 3 disclosure to be defensible rather than a token estimate. For SBTi validation, scope 3 must sit inside your target boundary when it is over 40% of total emissions — which, for the average organisation, it almost always is.

Organisations face increasing pressure from investors, tender authorities and major customers to report scope 3 emissions. A specialist helps organisations turn that pressure into a clear, prioritised plan to reduce scope 3 emissions rather than a scramble before each deadline. The goal is to tackle scope 3 emissions methodically, starting with the value chain emissions that matter most to your stakeholders.

The 15 GHG Protocol categories

Scope 3 includes 15 categories under the Greenhouse Gas Protocol, the global standard for GHG emissions accounting. A specialist maps, measures and quantifies your emissions across all of them — purchased goods and services, capital goods, fuel- and energy-related activities, upstream and downstream transportation, waste, business travel, employee commuting, leased assets, use and end-of-life of sold products, franchises and investments — and identifies which categories are material for your business.

In practice, a few relevant categories usually dominate — purchased goods and services for a manufacturer, transportation and use of sold products for a retailer. Knowing your hotspots early focuses effort where it changes the number.

Spend-based to activity-based calculation

There are two main ways to quantify scope 3 emissions, and most organisations move from one to the other as their data improves.

• Spend-based — your procurement spend (£) multiplied by an industry-average emissions factor per £. Quick, lower-precision, and acceptable for a defensible first-year footprint when primary data is thin. Spend-based data is the usual starting point for scope 3 reporting.
• Activity-based — physical quantities (tonnes of steel, kWh, km of freight) multiplied by activity-specific factors. Higher precision, and required for SBTi validation on material categories.

A typical path is spend-based in year one, then a primary-data collection plan targeting your most material categories and largest suppliers in year two. This staged approach keeps carbon accounting proportionate while steadily raising data quality — the rating CDP looks for against each category.

Method	Data used	Precision	Best for
Spend-based	Procurement spend (£) × factor per £	Lower	First-year footprint, broad coverage
Activity-based	Physical quantities × specific factors	Higher	Material categories, SBTi validation

A typical path moves from spend-based in year one to activity-based on your material categories in year two. See our scope 3 emissions guide and check current factors with the DEFRA conversion factors tool.

Supply chain and supplier engagement

Because so much of scope 3 is supply chain carbon, reducing it depends on supply chain engagement and direct supplier engagement. A specialist can provide a tested protocol — a template letter, a follow-up cadence and an escalation path — to lift primary-data response rates from your most material suppliers over successive reporting cycles. Sustainable procurement policies, supplier scorecards and contract clauses then turn that engagement into long-term carbon reduction across the value chain.

This is also where the biggest reduction opportunities sit. Once you know which product life stages drive the most emissions, targeted strategies — switching materials, consolidating freight, designing out waste — move the total carbon down rather than re-stating it each year.

How scope 3 fits SECR, ESG and net zero

Scope 3 is voluntary under SECR (with the narrow exception of business travel in employee-owned vehicles, which sits inside the SECR boundary), but it is increasingly expected by the same investors, lenders and customers who read your wider ESG reporting. SECR thresholds remain turnover of £36m or more, a balance sheet of £18m or more, or 250 or more employees — meeting two of the three. The April 2025 Companies Act uplift moved the general "large" company definition to £54m and £27m, but the SECR thresholds did not move, so a company now classed as medium-sized can still be in scope.

A robust scope 3 inventory is also the foundation of a credible net zero strategy and a complete carbon footprint. It underpins science-based targets, supports your corporate sustainability objectives, and gives you carbon data you can stand behind in any disclosure or tender. Strong scope 3 data feeds straight into your net zero strategies and net zero targets, and it lifts your wider sustainability performance in the eyes of investors and rating agencies.

Sustainable procurement, supplier carbon assessments and product carbon footprints all build on the same inventory. Get the measurement right once and it serves your sustainability goals, your ESG reporting and your reduction targets for years to come. It also sits alongside your core SECR reporting.

How matching works

This site is free to use. Tell us about your organisation and we connect you with a single vetted, IEMA-qualified specialist who gets in touch within one working day to scope the work and give you a fixed-fee, no-obligation quote. Wherever you are on your sustainability journey, the right specialist can help organisations move from a first emissions assessment to a fully primary-data inventory. Want to gauge your position first? Try our free SECR eligibility checker, deadline calculator and carbon calculator before you commit to anything.