Scope 3 Emissions Estimator
for General
Estimate Scope 3 across the 15 GHG Protocol categories — spend-based to activity-based — with category screening for ESRS E1-6 and a data improvement narrative limited assurance reviewers will accept.
Scope 3 emissions, documented.
Not just estimated.
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Scope 3 emissions estimation for General
On most CSRD first-year files we work, Scope 3 is 70%+ of the carbon footprint and the weakest part of the disclosure. Not because the emissions are absent — they sit in supplier spend, freight invoices, employee commuting surveys, and the use phase of sold products. They are absent from the file because category screening happened late, spend-based factors got applied uniformly, and no one documented why this entity has Categories 1, 6 and 7 material rather than Categories 4, 9 and 11. ESRS E1-6 requires the gross Scope 3 number broken out by significant category. ESRS E1-7 requires the reduction plan that connects to it. Limited assurance under ISAE 3410 looks at both, plus the data improvement narrative — and that narrative is what most files miss.
The practical difficulty begins with category screening. Not all 15 categories will be material for every entity. GHG Protocol guidance recommends screening each category for size (estimated share of total Scope 3), influence (the entity's ability to reduce emissions), data availability, and stakeholder interest. Most entities find that two to four categories account for 80% or more of their Scope 3 total. For a services firm, Category 1 (purchased goods and services), Category 6 (business travel), and Category 7 (employee commuting) typically dominate. For a manufacturer, Category 1, Category 4 (upstream transport), Category 9 (downstream transport), and Category 11 (use of sold products) carry the weight. Spending time on immaterial categories wastes effort that should go toward improving data quality on the categories that matter.
A common assurance finding is that entities apply spend-based emission factors uniformly without documenting why they chose spend-based over activity-based methods. Spend-based methods (using economic input-output factors like those from DEFRA, ADEME, or the US EPA's EEIO model) are acceptable as a starting point, but they carry high uncertainty. Activity-based methods (using physical quantities like kWh, kg, or tonne-km paired with process-level emission factors) produce far more reliable estimates. Assurance providers under ISAE 3410 expect entities to demonstrate a data improvement plan, showing progression from spend-based to activity-based methods over reporting cycles. Another frequent finding is double counting between Scope 1 or Scope 2 and Scope 3 Category 3 (fuel and energy related activities not included in Scope 1 or 2). Entities that do not reconcile these boundaries produce inflated totals that do not survive limited assurance procedures.
When applying this estimator, start by listing your entity's five largest spend categories and mapping them to GHG Protocol categories. Run the screening criteria on each category, document your materiality rationale, then select the estimation method that matches available data. For spend-based estimates, use the most jurisdiction-appropriate emission factors (DEFRA for UK entities, ADEME for French, GEMIS for German). Record the factor source, vintage year, and any assumptions about currency conversion or inflation adjustment. Where supplier-specific data exists (energy bills, transport manifests, waste transfer notes), switch to activity-based calculation for those line items. This hybrid approach gives you defensible numbers that improve as your data collection matures.