How-to guide · Scope 3
How to Collect Supplier Emissions Data for Scope 3
A practical, step-by-step process for procurement and sustainability leads to gather primary emissions data from suppliers — from prioritising who to ask, to building the questionnaire, chasing responses and folding the results into your Scope 3 inventory.
The short answer
To collect supplier emissions data, start with the suppliers that matter most — those with the highest spend or estimated emissions — then send them a short, standardised questionnaire asking for primary activity data (electricity in kWh, fuel use, and, where they have it, a product or corporate footprint in tCO2e). Explain why you need it, set a clear deadline, support and chase responses, then validate what comes back and fill any gaps with emission factors. Finally, fold the primary data into your Scope 3 inventory so it replaces less accurate spend-based estimates. A platform like CarbonTool's supplier portal automates the survey, the chasing and the integration so you do not run the campaign from a spreadsheet.
Why supplier data matters for Scope 3
For most companies, the value chain (Scope 3) is the largest part of the carbon footprint, and purchased goods and services usually dominate it. When you first estimate Scope 3 you typically use spend-based factors — multiplying what you spent by an average emission factor for that category. That is a fine starting point, but it cannot show a real reduction: if a supplier decarbonises, your spend-based number does not move. Primary data collected directly from suppliers replaces those averages with supplier-specific figures, improves data quality, and lets you track genuine progress and engage your highest-impact suppliers on reductions. If you are still sizing the problem, the Scope 3 calculator gives you a spend-based baseline to prioritise from.
How to collect supplier emissions data: step by step
Follow these seven steps to run a supplier data-collection campaign that produces usable, auditable primary data rather than a pile of half-finished spreadsheets.
- 1
Prioritise suppliers by spend and emissions impact
You cannot survey everyone, so start where the impact is. Rank your suppliers by annual spend and by estimated emissions from your existing spend-based Scope 3 inventory, then focus on the top suppliers that account for the bulk of your purchased goods and services. A short list of high-impact suppliers usually covers most of the footprint, so target those first and leave the long tail on estimated factors.
- 2
Decide what data to request
Be explicit about the activity data you need and the units. For most suppliers that means electricity consumption in kWh, fuel use in litres or kWh, and a corporate or product carbon footprint in tCO2e if they already calculate one. Ask only for what you will actually use, define every field, and specify the reporting year so responses are comparable. Requesting precise units up front avoids a second round of clarifying emails.
- 3
Build or reuse a standardised supplier survey template
Use one consistent questionnaire for every supplier so the responses are comparable and easy to process. Reuse a recognised, GHG-Protocol-aligned template rather than reinventing it, include clear instructions and worked examples, and keep it short. A standardised template also means you can compare suppliers and roll the data up automatically instead of reconciling dozens of different spreadsheets by hand.
- 4
Frame the request around your targets and deadlines
Suppliers respond when they understand why you are asking. Explain that the data supports your climate targets and reporting obligations (such as CSRD or customer requests), name a clear submission deadline, and say how the data will be used and protected. A short note from procurement or a senior sponsor, rather than a cold form, signals that this matters to the commercial relationship.
- 5
Send, support, and chase responses
Distribute the questionnaire to the right contact at each supplier, offer help for those new to carbon reporting, and track who has responded. Send reminders before the deadline and follow up with non-responders. Expect that not everyone will reply on the first pass, so build in time for a chase cycle and keep a clear log of status by supplier so nothing falls through the cracks.
- 6
Validate responses and fill gaps with factors
Check returned data for plausibility — wrong units, missing fields or figures that look orders of magnitude off are common. Query anything that does not add up before you trust it. For suppliers that did not respond or could not provide primary data, fall back to spend-based or activity-based emission factors so your inventory stays complete, and record which figures are primary versus estimated.
- 7
Integrate primary data into your Scope 3 inventory
Fold the validated supplier data into your Scope 3 calculation, replacing the spend-based estimates for those suppliers with their primary figures and tagging the data-quality level for each. Keep the source, unit, emission factor and supplier reference against every value so the inventory is auditable. Storing it on one platform means you can reuse the data next year and measure real supplier reductions over time.
What a supplier emissions questionnaire should ask
Keep it short enough that a busy supplier can complete it, but specific enough to be useful. A good questionnaire asks for:
Reporting boundary and year
Which legal entity or site the data covers and the calendar or financial year it represents, so figures are comparable across suppliers.
Energy and fuel use (activity data)
Electricity in kWh, plus gas and other fuels in litres or kWh — the primary activity data you can apply emission factors to.
Corporate or product carbon footprint
Any Scope 1, 2 and (ideally) 3 figures in tCO2e the supplier already calculates, and whether they have been third-party verified.
Methodology and emission factors used
Which standard (GHG Protocol, ISO 14064) and factor sources they applied, so you can judge data quality and comparability.
Targets and reduction plans
Whether the supplier has science-based or other reduction targets — useful for engagement and for forecasting your own Scope 3 trajectory.
Contact and data confidence
A named contact for follow-up and the supplier's own confidence in each figure, which feeds your data-quality scoring.
How CarbonTool makes supplier data collection easy
Running this process from email and spreadsheets is where most campaigns stall. CarbonTool turns it into a managed workflow on the same data backbone as the rest of your reporting:
Supplier portal, not your inbox
Invite suppliers to a dedicated portal where they complete a standardised survey. You track status by supplier and send reminders without managing a spreadsheet of email threads.
200+ GHG-Protocol templates
Reuse expert emission-source templates so the questionnaire and the factors behind it are methodologically sound, instead of building the survey from scratch.
Automatic gap-filling with factors
Where a supplier cannot provide primary data, CarbonTool falls back to spend-based or activity-based factors so your Scope 3 inventory stays complete and consistent.
One data backbone for every framework
Primary supplier data flows into the same inventory you use for CSRD, VSME, GRI, CDP and PCAF, so you collect once and report everywhere with a full audit trail.
Audit trail on every figure
Each value carries its source, unit, emission factor and data-quality level — and a record of whether it is primary or estimated — so the numbers hold up under assurance.
Reuse data year over year
Stored supplier responses and contacts roll forward, so next year's campaign is a refresh rather than a restart, and you can measure real supplier reductions over time.
See how it fits together in the supply chain module, compare the dedicated supplier emissions data collection software, or read our guide to the best Scope 3 emissions software.
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Start with the suppliers that drive most of your Scope 3 footprint — usually the ones with the highest spend or the highest estimated emissions in your existing spend-based inventory. A relatively small number of suppliers typically accounts for the majority of purchased goods and services emissions, so prioritising them gives you the biggest data-quality improvement for the least effort. Leave the long tail of small suppliers on estimated emission factors.
Ask for primary activity data with clear units: electricity consumption in kWh, fuel use in litres or kWh, and any corporate or product carbon footprint in tCO2e the supplier already calculates. Also capture the reporting year and boundary, the methodology and emission factors they used, whether figures are third-party verified, any reduction targets, and a named contact. Define every field and keep the survey short so a busy supplier can actually complete it.
Do not let your inventory stall. For suppliers that cannot or will not provide primary data, fall back to spend-based or activity-based emission factors so the figure is still complete, and tag it as an estimate rather than primary data. Offer support or a simpler version of the survey to suppliers new to carbon reporting, and re-approach them next year — engagement usually improves once the first request has landed.
Frame the request around why it matters: your climate targets, reporting obligations such as CSRD, or customer requirements. Send it from procurement or a senior sponsor rather than a cold form, set a clear deadline, keep the questionnaire short and standardised, offer help, and chase non-responders with reminders. Using a supplier portal that tracks status and sends automated reminders, like CarbonTool, removes most of the manual chasing that causes campaigns to stall.
Use primary data — collected directly from suppliers — for your highest-impact suppliers, because it improves data quality and is the only way to capture a supplier actually decarbonising. Use estimated spend-based or activity-based factors for the long tail of smaller suppliers and as a complete-coverage fallback where primary data is not available. A good inventory blends both and records the data-quality level of every figure.
Keep supplier responses on one platform rather than in scattered spreadsheets, with the source, unit, emission factor and data-quality level recorded against every figure. That makes each value auditable and lets contacts and prior submissions roll forward, so next year is a refresh rather than a fresh start. CarbonTool stores supplier data on the same backbone as your CSRD, VSME and CDP reporting so it is reused everywhere.
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