How to use primary data to improve your scope 3 accuracy

Less than 1 minutemin

11 July 2026

Scope 3 emissions are notoriously difficult to measure accurately, and most organizations know it. They represent the bulk of a company’s carbon footprint, yet they sit largely outside your direct control, buried deep in supply chains, product use phases, and end-of-life processes. The result? A lot of companies rely on estimates that are, frankly, not very precise. If you’re serious about scope 3 accuracy, the single biggest improvement you can make is shifting from secondary data to primary data wherever it counts most.

This isn’t about achieving perfection overnight. It’s about understanding where your biggest data gaps are, how to close them strategically, and what the process actually looks like in practice. Whether you’re preparing for CSRD reporting, working toward an SBTi target, or simply trying to give stakeholders a more honest picture of your supply chain emissions, better data makes everything downstream more credible.

Why secondary data falls short for scope 3

Secondary data, typically industry averages, spend-based emission factors, or database estimates, is a perfectly reasonable starting point. When you’re building your first scope 3 inventory and have no supplier data to speak of, these figures help you get a rough picture of where emissions are concentrated across your value chain. The problem is that they stay rough, often frustratingly so.

Industry averages describe a hypothetical average supplier, not your actual ones. A steel supplier that has invested heavily in low-carbon production will have a very different emissions profile from one that hasn’t, but spend-based factors treat them identically. Over time, this creates a growing disconnect between your reported figures and reality, especially as your suppliers make genuine progress on decarbonization. It also means that when you set reduction targets or report against them, you’re working with numbers that may not reflect what’s actually happening in your supply chain.

For frameworks like the GHG Protocol Scope 3 Standard, primary data is explicitly preferred for higher-accuracy reporting. As regulatory expectations tighten under frameworks like CSRD, the tolerance for imprecise estimates is shrinking. Secondary data will always have a role, but building a credible scope 3 reporting process means knowing when it’s no longer good enough.

Where primary data makes the biggest difference

Not every scope 3 category justifies the effort of primary data collection. The goal is to focus your resources where the accuracy gains are largest and the emissions volumes are highest.

Purchased goods and services (Category 1): This is typically the largest scope 3 category for most companies. Switching even a handful of key suppliers from spend-based estimates to actual emissions data can dramatically improve the accuracy of your total inventory.
Business travel and employee commuting (Categories 6 and 7): These are relatively straightforward to collect primary data on, since the information often already exists in HR or travel management systems. Actual distance and transport mode data beats generic averages easily.
Use of sold products (Category 11): For companies selling energy-consuming products, real-world usage data from customers or product testing gives far more reliable figures than assumed usage patterns.
Upstream transportation and distribution (Category 4): Logistics partners often have emissions data available, especially larger carriers who are themselves under reporting pressure. Requesting actual fuel consumption or tonne-kilometre data is increasingly realistic.

The common thread across all of these is that primary data doesn’t just improve accuracy in isolation. It gives you a foundation for tracking real change over time. When a supplier genuinely reduces their emissions, primary data captures that progress. Secondary factors don’t. That distinction matters enormously when you’re trying to demonstrate progress against an SBTi-aligned target or preparing a CDP submission.

How to collect primary data from suppliers

Supplier engagement is where scope 3 data collection gets practical, and admittedly, a little challenging. The good news is that more suppliers than ever are familiar with emissions reporting requests, particularly those who are themselves navigating CSRD requirements or working with large customers who have already asked for this data.

Start with your most significant suppliers

A tiered approach works well here. Identify the suppliers that account for the largest share of your purchased goods and services emissions, and prioritize them for primary data requests. Trying to collect data from hundreds of suppliers simultaneously is a recipe for low response rates and a lot of frustration. Starting with your top 20 or 30 by spend gives you meaningful coverage without overwhelming your team or your suppliers.

Be specific about what you’re asking for

Vague requests get vague responses. When you reach out to suppliers, be clear about the specific data you need: total greenhouse gas emissions for the goods or services they supply to you, the methodology they used to calculate it, and the reporting period it covers. Providing a simple template reduces the burden on suppliers and makes the data you receive far easier to work with.

Make it a relationship, not just a request

Suppliers are more likely to engage when they understand why you’re asking and what you’ll do with the data. Framing the conversation around shared goals, such as joint decarbonization, supply chain resilience, or meeting customer expectations, tends to get a better response than a compliance-driven demand. Some suppliers may also need support understanding how to calculate or report their own emissions, which is worth factoring into your engagement plan.

Building a reliable primary data pipeline from suppliers takes time, but even partial coverage in your highest-emission categories can meaningfully shift the quality of your scope 3 inventory. Once you have that data, the next step is knowing how to actually use it.

Integrating primary data into your scope 3 calculations

Collecting primary data is only half the job. Integrating it correctly into your GHG Protocol scope 3 calculations requires careful handling to avoid introducing new errors while trying to fix old ones.

The key principle is consistency. When you replace a secondary emission factor with a supplier-specific figure, you need to document the source, the methodology behind it, and the reporting period it covers. This matters both for internal quality control and for external assurance processes. Auditors and verifiers will want to understand exactly where each data point came from and how it was applied.

It’s also worth being deliberate about how you handle the transition from secondary to primary data year over year. A sudden drop in reported emissions because you’ve switched from a generic factor to a more accurate one can look misleading without proper context. Many organizations choose to restate prior-year figures when significant methodology changes occur, which keeps your trend data meaningful and defensible.

Finally, primary data from suppliers should be validated before use. Check that the figures are plausible relative to the scale of the goods or services provided, that the methodology aligns with recognized standards, and that the reporting boundary is what you expect. A supplier figure that includes emissions you’ve already counted elsewhere, or excludes something you assumed was included, can create double counting or gaps.

Common challenges and how to overcome them

Even with the best intentions, primary data collection runs into obstacles. Knowing the most common ones in advance makes them easier to navigate.

Low supplier response rates: This is the most common frustration. Improving response rates usually comes down to relationship quality, the simplicity of your request, and whether suppliers see a reason to engage. Tying data requests to procurement criteria or offering support to suppliers who lack internal capacity can both help.
Inconsistent methodologies across suppliers: When suppliers calculate their own emissions differently, the data becomes hard to compare or aggregate. Providing clear guidance on preferred methodology upfront, ideally aligned with the GHG Protocol, reduces this problem significantly.
Data gaps in specific categories: Some scope 3 categories are genuinely difficult to get primary data for, particularly downstream ones like end-of-life treatment of sold products. In these cases, a hybrid approach using primary data where available and secondary data for the rest is both practical and acceptable under the GHG Protocol.
Internal capacity constraints: Managing supplier data collection, validation, and integration is resource-intensive. Organizations that underestimate this often find the process stalling after the initial push.

What ties these challenges together is that none of them are insurmountable, but they do require a realistic plan. The organizations that make the most progress on scope 3 accuracy tend to treat it as an ongoing program rather than a one-time project. Building the systems, relationships, and internal knowledge to handle primary data well pays off over multiple reporting cycles.

When to bring in a scope 3 specialist

There’s a point in most scope 3 programs where the complexity of primary data collection and integration exceeds what a generalist sustainability team can handle efficiently. That’s not a failure; it’s just a sign that the work has matured to a level that benefits from specialist expertise.

Scope 3 emissions reduction consultants and LCA specialists, for example, bring deep technical knowledge of how to design data collection processes, validate supplier figures, and apply the GHG Protocol correctly in complex situations. This is quite different from what a CSRD reporting expert or a generalist sustainability consultant focuses on, so it’s worth being clear about the specific skills you need before bringing someone in.

Specialist support tends to be most valuable at a few key moments: when you’re setting up your primary data collection process for the first time, when you’re preparing for external assurance of your scope 3 figures, or when you’ve hit a specific technical challenge that your team doesn’t have the background to resolve. Having someone who has solved the same problem across multiple organizations can save a significant amount of time and prevent costly mistakes in your reported data.

Ready to sharpen your scope 3 data?

Improving scope 3 accuracy through primary data is one of the most impactful things an organization can do for its emissions reporting, but it’s also one of the more technically demanding. If your team is ready to take that step and could use expert guidance to do it well, we’re here to help.

At Dazzle, we match organizations with pre-screened sustainability freelancers who specialize in exactly this kind of work, from scope 3 data strategy to supplier engagement programs and GHG Protocol methodology. Whether you need someone for a focused project or ongoing support, we can connect you with the right expert within 48 hours. No long procurement processes, no agency overhead. Just the right person, ready to get started.

Reach out to our team and tell us what you’re working on. We’ll take it from there.

If you’re interested in learning more, contact our team of experts today.