Scope 3 Carbon Calculator — All 15 GHG Protocol Categories
The UK's most comprehensive free Scope 3 screening tool. Calculate emissions across all 15 upstream and downstream categories using DEFRA 2024/25 factors. Identify hotspots, screen for SBTi V2 materiality, and prioritise your value chain.
About the Scope 3 Carbon Calculator
Scope 3 emissions typically account for 70–90% of an organisation's total carbon footprint, yet they remain the hardest to measure. The RSustain Scope 3 Carbon Calculator is a free, comprehensive screening tool that covers all 15 categories defined by the GHG Protocol Corporate Value Chain (Scope 3) Standard.
Unlike simplified carbon calculators that lump all indirect emissions together, this tool separates upstream and downstream categories — from purchased goods and services (Category 1) through to investments (Category 15). Each category uses UK-specific DEFRA 2024/25 emission factors at the sector-tier level, giving you a more realistic screening estimate than single-rate approximations.
The tool automatically flags categories that exceed the SBTi V2 materiality threshold of 5% of total Scope 3, helping organisations identify which value chain categories require dedicated reduction targets under the Science Based Targets initiative's new standard. Each entry is tagged with a data quality indicator — Screening (spend-based), Enhanced (activity-based), or Primary (supplier-specific) — so you can track your measurement maturity alongside your emissions.
For organisations ready to move beyond screening estimates, the Pro tier unlocks activity-based calculations for business travel, employee commuting, upstream transport, and waste — each using precise DEFRA km-based or tonne-based factors. Pro users also gain access to 200+ granular DEFRA spend-based factors by SIC sector code, supplier-specific factor overrides, year-on-year comparison, and SECR/UK SRS/CSRD-aligned PDF reports with company branding.
Whether you are preparing for SECR reporting, building an SBTi transition plan, or undertaking a full carbon accounting exercise, this tool provides the essential first step: understanding where your Scope 3 emissions actually sit and which categories deserve priority action. Try our Carbon Diagnostic for a broader assessment or explore our Net Zero advisory for a complete decarbonisation strategy.
Scope 3 covers all indirect emissions that occur in a company's value chain, both upstream (supply chain) and downstream (product use and disposal). The GHG Protocol divides Scope 3 into 15 categories. Unlike Scope 1 (direct emissions from owned assets) and Scope 2 (purchased electricity), Scope 3 emissions are outside your direct operational control but typically represent the largest share of your carbon footprint — often 70–90% of total emissions.
The GHG Protocol defines 15 Scope 3 categories. Categories 1–8 are upstream (supply chain activities), and Categories 9–15 are downstream (activities related to sold products and services). Not all categories are relevant to every organisation — a services company may have negligible Category 10 (Processing of Sold Products), while a manufacturer will likely find Categories 1 and 11 dominant.
Spend-based emission factors convert procurement expenditure (in GBP) into estimated greenhouse gas emissions (kgCO2e). DEFRA publishes sector-level spend-based factors that reflect the average carbon intensity of goods and services in different economic sectors. While less precise than activity-based or supplier-specific data, spend-based factors are the recommended starting point for Scope 3 screening because procurement data is readily available from finance systems.
Under the SBTi's updated standard (V2), companies categorised as "Category A" must set near-term science-based targets for any Scope 3 category that represents more than 5% of their total Scope 3 emissions. This materiality threshold ensures that organisations focus reduction efforts on the categories with the greatest climate impact, rather than spreading resources across negligible sources.
Spend-based estimates are the least precise method in the GHG Protocol hierarchy but are suitable for initial screening and hotspot identification. They typically carry an uncertainty range of ±50–100%. The GHG Protocol recommends progressing from spend-based (screening) to activity-based (enhanced) to supplier-specific (primary) data over time, particularly for material categories. This calculator flags data quality level per category to help you plan that transition.
Screening data uses spend-based or average emission factors to estimate emissions from financial records. Enhanced data uses activity-based calculations (e.g., kilometres travelled, tonnes of waste) with published emission factors. Primary data comes directly from suppliers or direct measurement, offering the highest accuracy. The GHG Protocol encourages organisations to improve data quality over time, especially for material categories exceeding the SBTi 5% threshold.
The GHG Protocol requires companies to report on all categories that are relevant to their operations. Categories can be excluded only if they are demonstrably not applicable (e.g., a company with no franchises can exclude Category 14) or are below a de minimis threshold. SBTi V2 requires targets for categories exceeding 5% of total Scope 3. SECR requires disclosure of material Scope 3 where practical. This tool lets you mark categories as "not applicable" with a reason, which is the correct approach for transparent reporting.
SECR (Streamlined Energy and Carbon Reporting) requires qualifying UK companies to report Scope 1, Scope 2, and at least one intensity metric, with Scope 3 disclosure encouraged where practical. The upcoming UK Sustainability Reporting Standards (UK SRS) will align more closely with ISSB and require climate-related disclosures including material Scope 3. This calculator provides a structured screening across all 15 categories, helping you identify which Scope 3 sources are material and should be included in your annual report.