Overview
Sumday’s Supplier-Specific Emission Factors make it easier to use real supplier data instead of industry averages in your Scope 3 reporting. This article explains how the factors are calculated, how they align with the GHG Protocol, and the key considerations and limitations to keep in mind when interpreting them.
Our Calculation Approach
Supplier-specific emission factors in Sumday are calculated as:
Emission Factor (kg CO₂e per $ spent) =
Total reported GHG emissions (Scope 1 + Scope 2 + eligible Scope 3 Upstream) ÷ Operating Revenue
Key points:
The calculation uses the supplier’s publicly reported emissions and revenue from the same reporting year.
Emissions are converted to kg CO₂e and financial data to a common reporting currency.
The resulting factor represents the supplier’s corporate-level emissions intensity — the amount of GHG emitted per dollar of economic activity.
Factors are used in the Carbon Ledger to replace or complement spend-based industry averages, giving users a view of their suppliers’ relative emissions performance.
Alignment with the GHG Protocol
Sumday’s approach follows the hierarchy and allocation guidance in the GHG Protocol Corporate Value Chain (Scope 3) Standard:
1. Levels of supplier-specific data
The GHG Protocol recognises several data levels, in order of specificity:
Product-level data
Activity, process or production-line data
Facility-level data
Business-unit-level data
Corporate-level data
GHG Protocol Corporate Standard p. 80
While product-level or facility-level data provides the highest accuracy, corporate-level data still qualifies as supplier-specific under the standard. In practice, corporate data is often the only type currently available across suppliers.
2. Allocation approach
When suppliers do not provide product-specific emission factors, the Protocol allows reporting companies to allocate supplier emissions economically, using revenue as the basis.
This method is set out in Figure 8.2 and Box 8.2 of the Scope 3 Standard as an acceptable approach when other allocation metrics are unavailable.
Sumday’s formula (total emissions ÷ revenue) is therefore an example of economic allocation - a recognised method under the GHG Protocol.
Why Sumday Uses This Approach
Practicality and transparency – Product-level data and Product Carbon Footprints (PCFs) are still limited. Using corporate-level data ensures coverage today, with full traceability to public sources.
Consistency – Revenue-normalised factors enable comparison across suppliers and industries.
Alignment with market practice – This approach mirrors methodologies adopted by other reporting organisations and accepted in third-party-assured disclosures.
Flexibility – Sumday provides data and tools, not prescriptive rules. Users and their advisors decide whether supplier-specific data or industry averages are most appropriate for their reporting.
Disclaimers and Limitations
While supplier-specific data is a valuable step towards higher-quality Scope 3 information, it’s important to understand its limitations:
Supplier data is not automatically more accurate.
Accuracy depends on how representative the supplier’s boundary and reporting scope are for the goods or services purchased.Corporate-level intensity ≠ product-level emissions.
The factor reflects overall company performance, not the footprint of a specific product or transaction.Boundary and scope differences affect comparability.
Suppliers may include or exclude different emission scopes or subsidiaries.Professional judgement is required.
Users should assess whether supplier-specific data is appropriate for their context and document the rationale in their Basis of Preparation.Data availability and quality vary.
Reported emissions may be unaudited or subject to different levels of assurance. Sumday displays assurance details and source links for transparency.
Transparency of the calculation in Sumday
For every supplier-specific emission factor in Sumday, you can view:
The source disclosure (with link and page reference)
Reporting year and boundary
Assurance level and auditor, if disclosed
Scopes included (1, 2, 3 upstream)
Operating revenue and currency
This transparency ensures users can evaluate data quality and make informed accounting decisions.
Key Takeaways
Sumday’s supplier-specific emission factors are calculated using publicly disclosed corporate emissions intensity (emissions ÷ revenue).
The approach follows the economic allocation method permitted under the GHG Protocol Scope 3 Standard.
Professional judgement remains essential — supplier data should be assessed case-by-case for relevance and accuracy.
The goal is to make using real supplier data practical, transparent, and traceable, supporting more credible Scope 3 reporting as the market evolves.