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Spend-based or supplier-specific? Your Scope 3 number is probably both
Most Scope 3 baselines start from a spend file, and most teams call the result spend-based and leave it there. That skips the part that matters. Spend is the input. What decides whether the number can be acted on is the emission factor you multiply it by, and that factor can be a sector average or it can belong to the organisation you actually bought from.
DitchCarbon provides verified emissions data for over 2 million organisations, so procurement, sustainability and finance teams can measure and act on supply chain and portfolio emissions from one source. This page sets out what separates the two, what each step up costs in time and effort, and which steps cost nothing at all.
What is the difference between spend-based and supplier-specific emissions data?
They describe two different things, which is why the comparison usually goes wrong. Spend-based describes what went into the calculation: money. Supplier-specific describes where the emission factor came from: the organisation you bought from, rather than an average for its sector.
The GHG Protocol Technical Guidance for Calculating Scope 3 Emissions defines its spend-based method as estimating emissions "by collecting data on the economic value of goods and services purchased and multiplying it by relevant secondary (e.g., industry average) emission factors". Secondary is the operative word. Once the factor comes from that organisation's own published inventory, the figure is no longer secondary data and it is no longer the guidance's spend-based method, even though your input is still a line of spend.
That distinction is the one the market keeps collapsing, and collapsing it is expensive, because it makes supplier-specific data sound like a project rather than a substitution. DitchCarbon holds three layers and uses all of them: company emissions data for over 2 million organisations, including corporate-level GHG inventories; supplier-specific emissions at spend, activity and product level; and a generic emission factor library drawn from ecoinvent, CEDA, EPA, DEFRA and EXIOBASE. The layer that produced a given line is recorded on that line.
Can a spend-based number be supplier-specific?
Yes, and for most of a supplier list it already can be today. The same spend file, multiplied by that organisation's own emission factor instead of the average for its sector, produces a figure that belongs to the supplier rather than to its industry.
The practical difference is what happens next year. A sector average is fixed for everybody in that sector, so a supplier that halves its emissions changes nothing in your baseline. An organisation-specific factor is derived from what that organisation published about itself, so when it reports a reduction, your number moves. Same file, same process, same effort, and a figure that now responds to the thing your programme exists to do.
DitchCarbon puts this in a single toggle. Switch the headline emissions figure to industry emission factors only, then switch it back to organisation factors where they exist, and the difference between the two numbers is the share of your baseline resting on what organisations actually published. It is a number on screen rather than a claim, and it takes nothing from your suppliers to produce.
What are the four calculation methods for Category 1?
The GHG Protocol names four for purchased goods and services, ordered by how specific each is to the individual supplier. The first two require data from the supplier. The second two use secondary data.
| Method | What you have to have | What the resulting number can support |
|---|---|---|
| Supplier-specific | Product-level cradle-to-gate inventory data from the supplier, for the product you bought | A figure tied to the item in your basket. It separates two suppliers selling the same thing, and it moves when that product's footprint changes |
| Hybrid | Allocated Scope 1 and 2 data from the supplier, plus secondary data to fill the rest | A figure tied to the supplier. It moves when that supplier decarbonises, and the allocation step is where its uncertainty sits |
| Average-data | The mass or other physical unit of what you bought, plus a secondary factor per unit | A figure tied to the physical thing rather than its price. It moves when you buy less or buy differently, not when the price changes |
| Spend-based | The money spent, plus a secondary factor per unit of currency, drawn from an environmentally extended input-output model | A total, and a ranking of where to look next. It cannot separate two suppliers in one sector, and it moves with price rather than with emissions |
Method names and definitions from the GHG Protocol Technical Guidance for Calculating Scope 3 Emissions, chapter 1, 2013.
The guidance sets its spend-based method as the fallback in the decision tree: if the other three are not feasible, "companies should apply the average spend-based method". It also expects the mix to change. The Scope 3 Standard says companies "should seek to improve the data quality of the inventory by replacing lower quality data with higher quality data as it becomes available", prioritising the activities carrying the most emissions. DitchCarbon is built for that replacement rather than for the first pass, which is why the method sits on every row and the rows still on a sector average are filterable as a group.
Is supplier-specific data always more accurate than a sector average?
No, and the GHG Protocol says so two pages after ranking the methods. Box 1.1 of the Technical Guidance states that the supplier-specific and hybrid methods "may not produce results that are a more accurate reflection of the product's contribution to the reporting company's scope 3 emissions. In fact, data collected from a supplier may actually be less accurate than industry-average data for a particular product." The reason it gives is allocation: splitting a supplier's total emissions across everything it sells "can add a considerable degree of uncertainty".
The four methods are ordered by specificity rather than by accuracy, and a page that presents them as an accuracy ladder is overstating what the standard says. The Scope 3 Standard makes the same point from the other direction: "In some cases, primary data may not be available or may not be of sufficient quality. In such cases, secondary data may be of higher quality than the available primary data for a given activity."
So the useful question is not which method wins in the abstract. It is which method produced each line of your own number, and whether you can see it. DitchCarbon marks every organisation with the method behind its figure, and the portfolio table filters on that marker, so the answer is a view you open rather than a reconstruction you commission.
What does each step up actually cost you?
Not the same amount, and the market talks about them as though it were. One step costs nothing and is available immediately. The two above it are worth taking on the lines that matter, and they take real time from your team and sometimes from your supplier. Being straight about which is which is how a programme gets sequenced properly.
| What the line is calculated on | What it takes from you | What it takes from your supplier | Does your number move when they cut emissions? |
|---|---|---|---|
| A sector average applied to spend | A spend file | Nothing | No. The factor belongs to the industry, so it is identical for every company in it. The only way to reduce this number is to spend less, which is why so many programmes stall here |
| The organisation's own emission factor applied to spend | The same spend file. Nothing extra. | Nothing, where it has already published something | Yes. The factor is derived from that organisation's own reported inventory, so a reduction it publishes shows up in your baseline. This is the step most teams do not realise is already available to them |
| Activity data | Consumption data for what was actually used, which is a real piece of work | Often has to supply it | Yes, and it separates two suppliers doing the same volume differently. Worth the effort on high-emission categories, and hard to justify across a whole tail |
| A published product carbon footprint | Allocating spend to named products, item by item | A published footprint for that item | Yes, at item level, and it is the only version that distinguishes two products from the same supplier. The most precise answer and the most expensive to reach |
Assessed August 2026 against the DitchCarbon platform.
Read the second row on its own. It is the one that changes a programme, because it moves a line from something you cannot act on to something you can without asking anybody for anything. DitchCarbon supplies it from what organisations have already published, matched to the legal entity, with the source document behind the figure and the assurance status recorded separately for each scope.
The two rows below it are better and more expensive, and DitchCarbon supports both. Allocate spend to a named product and that product's own published footprint is used for the allocated part, carrying kgCO2e per unit, the standard it was prepared to, the third-party verifier where there is one, whether the boundary is cradle to gate or cradle to grave, and a quality score. The rest of the spend calculates on the organisation factor, with units, kgCO2e, spend and share of the total on the same line, so the two methods sit side by side rather than one hiding the other. Spend that work where the emissions are, and let the second row carry the tail.
Why can a sector average not be acted on?
Because it moves with price. A figure built from a sector average is your invoice multiplied by an industry rate, so paying more produces more emissions and paying less produces fewer, whatever the supplier is doing.
The GHG Protocol's own consultation records this. Its October 2024 discussion paper on inventory quality reports respondents noting that the method is "not reliable for tracking or differentiating value chain performance. For example, a company that pays a higher price for high-quality components or materials may calculate higher GHG emissions when using generic environmentally-extended input output (EEIO) emission factors." The Scope 3 Standard itself warns that "spend and revenue may not correlate well with emissions".
The consequence shows up in what teams believe they can do next. In the SBTi's corporate survey published in February 2023, 57% of respondents said that under a spend-based methodology the only way to decarbonise is to reduce the procurement budget. The same survey found 6% of respondents using supplier-specific emission factors and 94% relying on secondary data, a figure the GHG Protocol later cited in its own discussion paper.
That is a factor problem rather than a spend problem, and it is fixable without changing how you calculate. Swap the industry rate for the organisation's own factor on every supplier that has published one, and the same spend file starts responding to what your suppliers do. DitchCarbon shows you both numbers so the size of the change is visible before you commit to it.
Do CSRD and CDP require you to say which method you used?
CDP does, per category. Question 7.8.3 asks for the calculation methodology by name, from a picklist mirroring the GHG Protocol's method names, and 7.8.4 asks for the "percentage of emissions calculated using data obtained from suppliers or value chain partners".
Under CSRD the answer depends on the reporting year, and it is about to change. The ESRS in force, adopted 31 July 2023, require an undertaking to "disclose the percentage of emissions calculated using primary data obtained from suppliers or other value chain partners", at ESRS E1 AR 46(g), along with the calculation methods used for each significant Scope 3 category. The revised ESRS adopted by the Commission on 3 July 2026, applying to financial years beginning on or after 1 January 2027, drop that percentage requirement and name "spend-based data" in the body of ESRS 1 among the inputs an undertaking may use where it cannot collect value chain information.
So the obligation tightens for the current year and loosens for the next, and the requirement is not the reason to hold the number. A baseline whose method mix you cannot state is one you cannot make auditable, and the mix is what tells you whether last year's reduction was real or a procurement saving. DitchCarbon reports it as a proportion of the total, split across organisation, industry, product and activity data, rather than as something reconstructed a year later under audit.
How much of a supplier list already has an organisation-specific factor?
More than most teams expect, because the work of finding published disclosures has already been done. DitchCarbon covers over 2 million organisations, and a recent deployment reached about 60% of a large supplier base within 2 weeks.
The list a procurement team actually holds is a spend export rather than a clean supplier register, with duplicates, trading names and entities that no longer exist. That is the file the import expects, in CSV or Excel, with no cleanse and no integration project first. Rows resolve against DUNS, LEI and ISIN identifiers where those are present and against name, domain and email where they are not, and parent and subsidiary relationships are resolved as well, so a figure attaches to the entity you buy from rather than the group above it. The import history records how many rows were processed, so a partial match reads as a number rather than a surprise.
Requests are for what is left over. The maturity ladder sorts organisations against embodied emissions across four steps, from not disclosing through to leading with product carbon footprints, so a supplier carrying a large share of your footprint and sitting on the bottom step is the first conversation rather than the fiftieth. The organisation being asked reviews a profile already populated from its own published reports instead of completing a blank form, which is why a prepopulated request gets a better response rate than a cold survey. That order is the product: DitchCarbon starts from what has already been published, and asks only where an answer would change the total. Numbers you can defend within 2 weeks.
What if you are the supplier being estimated?
If your organisation has not published emissions, your customers are not leaving you out of their Category 1 total. They are estimating you from your sector and what they spent with you, and that figure sits in their supplier scorecard whether or not you have seen it.
Your DitchCarbon profile already exists and already carries whatever you have published, listed by year with the assurance provider and standard found for each scope, and the document each figure came from. A disclosure to-do list shows year by year what is held on you, marked complete or partial, and names the categories buyers expect and cannot find. Upload an assurance statement or an updated report and we extract from it rather than asking you to retype figures you have already published, and where extraction has read something wrongly there is a route to say so. Answer the questions buyers ask most often once, and any logged-in viewer from another organisation reads the same answer rather than sending you another form. It is free, and there is no fixed form to complete. Claim your profile.
How do you find out where your own baseline stands today?
Three questions, answerable against the number you already have.
What share of the total was calculated on a sector average rather than on a factor belonging to the organisation itself? Can you produce the method for any single line without rebuilding the model? And if your largest supplier halved its emissions tomorrow, would your figure move?
The third question settles it. On a sector average the answer is no, and the reduction shows up only when procurement spends less.
A coverage check answers all three on a representative sample of your own suppliers: how many of them already carry a factor derived from what they published themselves, the source document behind each, and what is left resting on an industry average. Send a sample to the coverage check.
Last reviewed August 2026.
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