How to move from spend-based Scope 3 estimates to supplier-specific data

Published 30 October 2026

How can a large company move from spend-based Scope 3 estimates to supplier-specific emissions data?

Keep the spend file and change the factor, and the line starts moving when the supplier cuts its emissions. A spend-based line is spend multiplied by a sector average; replace that average with the supplier's own emission factor, taken from the inventory it has already published, and the same line becomes supplier-specific (primary) emissions data. DitchCarbon holds verified emissions data for over 2 million organisations, built on primary emissions data wherever it exists, so for most of a large company's supplier list that step costs nothing beyond the spend file it already has, and asks nothing of the suppliers.

The next two steps cost real effort and belong on the lines that carry the emissions: activity data (what was actually consumed or bought, in kWh, litres, tonnes or units) and product carbon footprints for named items. Every line records which method produced it, so the share of the baseline still on a sector average is a number you can watch fall.

Is spend-based data the problem?

The sector average is the problem, as our spend-based versus supplier-specific comparison sets out. Spend is an input, and the same spend can be calculated two ways. Multiplied by a sector average, the line moves only when procurement spends less, so it cannot show a supplier's reduction. Multiplied by that supplier's own factor, the line moves when the supplier cuts its emissions.

The GHG Protocol's Scope 3 guidance defines its spend-based method as spend multiplied by secondary emission factors, which are industry averages. Once the factor comes from the supplier's own reported inventory it is primary data, so the line has left the spend-based method even though its input is still a line of spend. That distinction is what turns supplier-specific data from a project into a substitution.

What are the steps from spend-based to supplier-specific data?

Four rungs, and they do not cost the same. Our guide to primary and spend-based data covers the trade-off in more depth.

The second rung is the one most teams do not know is available, and it is where most of a list can move first. DitchCarbon calculates on product data, activity data and supplier-specific spend, and only when all else fails, industry-level spend. One supplier can sit on several rungs at once: a product footprint for the item you buy most, its own factor on the rest of your spend with it.

Which suppliers should move up first?

The ones carrying the most embodied emissions, which is a different list from the ones with the most spend. A small invoice in a carbon-intensive sector can outweigh a large one in a light sector, so rank on emissions before deciding where effort goes.

Then read that list against disclosure. A supplier that already publishes an inventory moves to the second rung with no request at all. A supplier carrying a large share of your footprint and publishing nothing is the highest-value request you can send. DitchCarbon sorts suppliers on a four-step maturity ladder against embodied emissions, so both groups are visible on day one.

How do you reduce reliance on estimated Scope 3 data and get real supplier numbers?

Start with the numbers suppliers have already published, then ask only for what is missing. Published GHG inventories, CDP responses and product carbon footprints are primary data under the GHG Protocol, and for a large supplier list a lot of them already exist. A recent DitchCarbon deployment reached 70% coverage of emissions with primary data within 2 weeks.

For the suppliers that matter and have published nothing you can use, the request goes out prepopulated with what DitchCarbon already holds on them, asking only for the detail you need: a site's energy use, the activity data behind what you buy, a footprint for a named product. The supplier adds that detail to its own figures, which is a smaller job than a blank survey. How to collect supplier emissions data covers the request in detail. Where nothing comes back, the line stays on a sector average and says so.

What does an auditor need to see when the method changes?

The method behind every line, and a record of when it changed. Moving a supplier from a sector average to its own factor changes the number, sometimes by a lot, and an auditor will want to separate that methodology change from a real reduction. The GHG Protocol expects a base year recalculation policy for exactly this case.

DitchCarbon records the method on every line and keeps each figure's source and change history, so a movement can be traced to the document behind it. The Portal calculator is verified to ISO 14064-3, limited assurance, by UL Solutions, renewed annually, and the report is downloadable from the trust centre.

How long does the move take?

The first rung change takes as long as matching the spend file to the right organisations. With DitchCarbon, numbers you can defend within 2 weeks is the timeline for a baseline where every supplier with a published inventory is already on its own factor. Matching runs on entity resolution against DUNS, LEI and ISIN identifiers, and works from a company name alone where that is all the file holds.

Activity and product data take longer, because they depend on suppliers and on your own purchase records carrying quantities and product codes. Plan them over reporting cycles, on the lines where they change a decision, and let the share of the baseline still on a sector average be the measure of progress.

Being asked for this data yourself?

If your customers or investors are asking you for emissions data, the same logic runs in reverse: your published figures are what they can use first. Claim your company profile to answer once and reuse it for every request.