Scope 3 Emissions: Spend-Based vs Supplier-Specific Data

Scope 3 emissions are where the majority of  organisations’ carbon footprint live. For most businesses, particularly those in procurement-heavy industries, purchased goods and services alone can account for 70% or more of total emissions. Yet this is precisely the category where data quality is weakest, methodology choices are most consequential, and regulatory expectations are tightening fastest. 

In 2026, procurement heads and sustainability managers are navigating a sharper question than ever before: should we be using spend-based or supplier-specific data to calculate our Scope 3 supply chain emissions? And critically, what do AASB S2, CSRD, and UK SRS expect? 

This guide cuts through the complexity. 

What is spend-based emissions data? 

The spend-based method estimates supplier emissions by multiplying the monetary value of goods or services purchased from a supplier by an emissions intensity factor, typically expressed in kgCO2e per unit of currency spent (for example, per pound or Australian dollar). 

These intensity factors are drawn from economic input-output databases such as the UK’s DEFRA emission factors, the US EPA’s USEEIO model, or EXIOBASE for multi-regional coverage. 

When spend-based works well: 

• Early-stage Scope 3 reporting where supplier engagement has not yet been established 

• Long-tail suppliers (Categories 1 and 2 of the GHG Protocol Scope 3 Standard) where the emissions contribution is minor and engagement ROI is low 

• Categories where verified activity data is genuinely unavailable 

• Providing an initial carbon footprint baseline when beginning your supply chain emissions journey 

Its limitations are significant, however. Spend-based data is inherently imprecise. The same monetary spend on two suppliers in the same sector can represent vastly different actual emissions depending on their energy mix, geographic location, operational efficiency, and product type. A supplier running on 100% renewables in Queensland looks identical to a coal-dependent competitor, if you are relying on spend figures alone. 

Spend-based data also provides no decarbonisation signal. It cannot reflect real emissions reductions a supplier has made, and it is sensitive to price fluctuations: if a supplier raises their prices, your spend-based emissions go up even though nothing has physically changed. 

For audit purposes, spend-based data is increasingly viewed as an estimate of last resort, rather than a methodology of choice. 

What is supplier-specific emissions data? 

Supplier-specific data , also referred to as primary emissions data , is calculated using real operational information provided directly by the supplier: energy consumption, fuel use, vehicle fleet, refrigerant usage, and more. These inputs are then converted to tCO2e (tonnes of CO2 equivalent) using regionally appropriate GHG emission factors. 

Where a supplier calculates emissions using their own operational inputs (for example, kWh of electricity multiplied by a regional grid factor), this is known as the activity-based method. Alternatively, some suppliers provide pre-calculated figures drawn from their own verified GHG inventory or a CDP disclosure. Both approaches fall under the supplier-specific umbrella and represent the highest-quality Scope 3 data available to reporting organisations. 

 GHG Protocol Scope 3 Standard generally considers this methodology as the highest-quality form of Scope 3 data when they are complete, methodologically robust, and independently verified where possible… It reflects what actually happened in the supplier’s operations, not a statistical proxy. 

Why suppliers have historically resisted it: 

The problem has never been methodology. It has been admin burden. As we explored in Your suppliers are not going to fill in that Scope 3 spreadsheet, the traditional model asks suppliers to reformat the same data repeatedly for every customer who sends a spreadsheet. For a mid-sized supplier with 20 enterprise customers, that is 20 different templates, 20 different deadlines, and 20 different definitions of what is needed. It is not a data problem. It is a system design problem. 

The solution is not to abandon supplier-specific data. It is to change how suppliers submit it. 

Accuracy trade-offs: a head-to-head comparison 

The accuracy gap matters beyond compliance. If a supplier improves their energy efficiency or switches to renewables, spend-based data will never capture it. Supplier-specific data will. That distinction is increasingly important as organisations move from reporting their emissions to reducing them. 

For more on the data quality dimension, see How to fix Scope 3 data quality issues. 

What the frameworks require in 2026 

CSRD and ESRS (EU and Ireland) 

The Corporate Sustainability Reporting Directive requires disclosure of Scope 3 emissions across all material categories. The EU’s Omnibus I package and Stop-the-Clock Directive, adopted in early 2025, significantly revised the original rollout. Wave 1 companies (large public-interest entities previously subject to the NFRD) are already reporting, with first disclosures covering FY2024. Wave 2 companies (large undertakings with more than 1,000 employees and over €450 million in turnover) now have until 2028 to publish their first report, covering FY2027, a two-year delay from the original timeline. The Omnibus changes also narrowed the total number of in-scope companies by over 80%, concentrating mandatory reporting on the largest enterprises meeting the revised thresholds. 

For those in scope, ESRS E1 specifies that organisations should use the most accurate data reasonably available and disclose the methodologies applied. Spend-based data is permissible where supplier engagement has not yet been established, but organisations are expected to demonstrate a trajectory toward higher-quality primary emissions data. Auditors under CSRD are required to provide limited assurance on sustainability disclosures from the first reporting year, which creates real pressure for defensible methodology. 

AASB S2 (Australia) 

Australia’s mandatory climate reporting regime, now in its first year with Group 2 entities entering from July 2026, is ISSB-aligned and expects Scope 3 disclosures to use the best available data. The AASB S2 standard does not prescribe a single methodology, but it requires entities to disclose their approach and any significant estimation uncertainty. Given that Group 2 includes many procurement-intensive businesses in construction, logistics, and professional services, the quality of supplier emissions data is directly material to disclosure accuracy. See our AASB S2 Group 2 guide for the full picture of what July 2026 requires. 

UK SRS 

The UK Sustainability Reporting Standards were published on 25 February 2026 by the Department for Business and Trade and are currently available for voluntary use. They are aligned with IFRS S1 and S2 and are the UK’s endorsed version of the ISSB global baseline standards. The FCA is consulting on making UK SRS mandatory for listed companies for financial years beginning on or after 1 January 2027, with final rules expected in autumn 2026. The government has also indicated a separate consultation on extending mandatory reporting to large private companies later in 2026. Like AASB S2, UK SRS is ISSB-based and requires climate-related disclosures, including Scope 3 where material. The expectation for data quality mirrors CSRD: spend-based estimates are acceptable as a starting point, but organisations are expected to build toward supplier-specific approaches, particularly for high-spend or high-emission categories. Read our UK SRS overview for more detail on scope and timelines. 

The consistent message across all three frameworks: spend-based data will keep you compliant today, but it will not keep you defensible tomorrow. Assurance requirements are tightening, and auditors under ISSA 5000 and equivalent standards are asking harder questions about the basis of Scope 3 figures. See Audit-ready carbon data for ISSA 5000 compliance for what that means in practice. 

Building a hybrid Scope 3 approach: practical steps for 2026 

No organisation needs to switch entirely from spend-based to supplier-specific overnight. The right approach is a structured transition, prioritised by materiality. 

Step 1: Identify your high-impact supplier categories 

Rank your supplier spend by category and overlay with sector-average emissions intensity. Your top 20% of suppliers by spend, or your highest-emissions categories, are where supplier-specific data will make the greatest difference to accuracy and auditability. Start there. 

Step 2: Keep spend-based for the long tail 

For hundreds of smaller suppliers in low-emissions categories, spend-based estimates remain a proportionate approach. Document your methodology clearly and disclose the estimated proportion of Scope 3 covered by each approach. All three frameworks accept this hybrid model. 

Step 3: Transition priority suppliers to activity-based data 

The shift from spend-based to supplier-specific does not require complex negotiations or bespoke data-sharing agreements. It requires a system that makes it easy for suppliers to submit their own activity data once and reuse it across all their customers. 

Step 4: Ensure regional emission factor accuracy 

One of the most common errors in Scope 3 reporting is applying the wrong emission factor to supplier data. A supplier in Western Australia operates on a very different grid to one in Victoria. A UK supplier’s electricity factor for 2026 differs significantly from 2023. Regional, annually updated GHG emission factors are not optional. They are essential for defensible carbon reporting. This is explored in depth in Why multi-site operations need regional emission factors. 

Step 5: Build for audit from the start 

Structure your supplier data collection so that every submission is traceable: who entered it, when, using which emission factor database, and what percentage was allocated to your organisation. That traceability is what separates a reportable Scope 3 figure from an estimate. See Automated carbon reporting: why audit controls matter for how to embed this into your process. 

How eco-shaper’s supplier portal solves the data collection problem 

The reason most organisations default to spend-based data is not preference. It is practicality. Getting suppliers to submit accurate activity data at scale has historically been a manual, low-response process. 

eco-shaper’s Supply Chain Engagement feature is built specifically to change that. Three things make it work for procurement teams at scale. 

First, supplier onboarding requires no manual chasing. Upload your supplier list individually or in bulk, and eco-shaper generates a personalised calculator link for each supplier automatically. A traffic light dashboard shows submission status across your entire supply chain at a glance, and all activity data flows directly into your enterprise Scope 3 report. 

Second, the experience is designed around the supplier, not the sustainability team. Each supplier receives a branded invitation email with one-click access to their own carbon calculator, covering energy, vehicles, equipment, and refrigerants. The platform automatically applies the correct regional emission factor from a database of 120,000 annually updated factors. Most suppliers complete their first submission in under 30 minutes. 

Third, and most importantly for data quality, the supplier’s account is theirs to keep. They submit once and allocate their total emissions across all customers by percentage. A supplier working with multiple enterprise customers enters their data once and apportions it accordingly. There is no re-entry, no bespoke spreadsheet for each buyer, and no reason to decline participation. 

The data privacy model matters too. Your Scope 3 dashboard receives only the supplier’s allocated tCO2e figure, their proportional share of your emissions, and not their full operational breakdown. Suppliers remain in full control of their detailed data, which removes a significant barrier to participation. 

This is supplier-specific Scope 3 data collection at scale: a platform where one supplier submission serves many customers, and every figure is audit-ready under the GHG Protocol Scope 3 Standard and ISO 14064-1. 

The bottom line for procurement and sustainability teams 

Spend-based data has its place. It is a reasonable starting point, appropriate for long-tail suppliers, and accepted by all three major frameworks as an interim methodology. But it has a ceiling, on accuracy, on auditability, and on its ability to reflect the actual emissions reductions your suppliers are making. 

The direction of travel across AASB S2, CSRD, and UK SRS is consistent: build toward supplier-specific, activity-based primary emissions data. Do it in a way that does not create an unbearable admin burden for your suppliers. Document your hybrid methodology clearly. 

The organisations best positioned for the next round of assurance requirements are the ones building supplier carbon data infrastructure now, not the ones trying to retrofit it under audit pressure in 2027. 

If you want to see what a structured supplier data system looks like in practice, explore eco-shaper’s Supply Chain Engagement feature. Or read about the business case for Scope 3 carbon tracking to understand the wider value beyond compliance. 

eco-shaper is a carbon accounting and sustainability reporting platform used by organisations across the UK &  Australia, and broader APAC. Our Supply Chain Engagement feature helps procurement teams collect audit-ready Scope 3 supplier data, without the spreadsheet admin.