Summary
Scope 3 is hard to measure because the emissions happen at suppliers and customers, so you depend on their data. That data is often missing, estimated or in different formats. Large companies overcome this by screening all categories first, focusing effort on the biggest hotspots, collecting supplier data step by step and documenting every assumption.
Last updated: 23 October 2026
Why does Scope 3 matter so much?
Scope 3 is usually most of a company's footprint, so a weak Scope 3 number means a weak footprint. In 2023 disclosures, supply chain emissions averaged 26 times operational (Scope 1 and 2) emissions, according to CDP and BCG (June 2024). For a full introduction, see our main guide to Scope 3 emissions.
Accurate Scope 3 data matters for four reasons:
- Disclosure. IFRS S2, Australia's AASB S2 and California's SB 253 all require Scope 3 after a transition period.
- Targets. Science-based targets need a reliable Scope 3 baseline.
- Customers. Large buyers ask suppliers for product and company emissions data.
- Risk. Scope 3 shows which inputs and suppliers are most exposed to carbon prices and supply shocks.
How many companies measure Scope 3 accurately?
Very few. In the 2024 BCG and CO2 AI survey of nearly 2,000 companies, only 9% said they comprehensively report Scope 1, 2 and 3 emissions. The gap is mostly a data problem, not a lack of will.
What are the main challenges in measuring Scope 3?
There are five common ones. The table sums them up, and the sections below explain each.
| Challenge | Why it happens | How to deal with it |
| Missing supplier data | Many suppliers don't measure emissions, or won't share | Start with spend-based estimates; ask the largest suppliers first |
| Estimates of estimates | Each tier of the chain uses averages and proxies | Replace averages with primary data in the hotspots |
| No common format | Suppliers use different methods, units and boundaries | Set one data request template and standard units |
| Long-tail value chains | Thousands of suppliers across many tiers | Rank suppliers by emissions; cover the top share, estimate the rest |
| Limited people and tools | Scope 3 needs carbon, procurement and data skills together | Centralise data and automate emission factor matching |
1. Suppliers don't have, or won't share, the data
Many suppliers, especially smaller ones and farms, don't measure their emissions. Those that do may treat the data as confidential or share it in a format you can't use. This is why most companies begin with secondary data: industry averages, government statistics and spend-based emission factors.
2. Estimates stack on top of estimates
In a long value chain, each step relies on estimates from the step before. Take a food processor buying crops from farmers. The farmers use fertiliser, and the fertiliser maker uses raw materials and energy. Every step adds emissions from production and transport, and each partner may use a different average or emission factor. Small errors at each step add up.
3. There is no single disclosure format
The GHG Protocol sets the accounting rules and the CDP provides questionnaires. But companies still choose different methods, boundaries and emission factors. Two suppliers making the same product can report very different figures for reasons that have nothing to do with their real performance.
4. The value chain has a long tail
Most Scope 3 often sits with a small group of suppliers and materials. But large enterprises also have thousands of smaller suppliers. Chasing data from all of them is not practical. The GHG Protocol allows you to estimate the long tail with secondary data, as long as you disclose how.
5. It takes skills most teams don't have yet
Scope 3 needs people who understand carbon accounting, procurement and data management, plus processes to check data quality. Many sustainability teams are small and rely on spreadsheets. That makes the work slow and hard to repeat each year.
How can large enterprises overcome these challenges?
Treat Scope 3 as a data improvement programme, not a one-off calculation. Get a full first estimate, then improve it where it matters most:
- Screen all 15 categories with spend and activity data to see which are material.
- Find the hotspots. Rank categories, materials and suppliers by emissions.
- Choose the right method for each hotspot. Move from spend-based to activity-based or supplier-specific data where emissions are highest. See our comparison of Scope 3 calculation methods.
- Engage the suppliers that matter. Ask the top suppliers for primary data and support them to provide it. See Scope 3 supplier engagement.
- Score and track data quality. Record which figures use primary data and which use averages, and set a goal to raise the primary share each year.
- Document everything. Keep a clear trail of sources, methods and emission factors so auditors can follow each number.
What does this look like for a real company?
iNova Pharmaceuticals worked with Terrascope to build its footprint and found that Scope 3 made up 99% of it. That result showed the team that its climate work had to focus on the value chain, not its own sites.
How Terrascope helps with Scope 3 measurement
Terrascope is a carbon management platform built for companies whose footprint is mostly Scope 3. It helps with each challenge above:
- Missing data: screens every category from spend and activity data, and uses AI to match each line to a suitable emission factor.
- Data quality: shows the quality of the data behind every result, so you know which figures to improve first.
- Formats and long tail: brings ERP, procurement and supplier files into one model with Terrascope data management.
- Supplier data: collects primary data from suppliers through Scope 3 supplier engagement tools.
- Audit: keeps a trail from source record to reported figure.
To find your largest Scope 3 categories before you invest in data collection, book a free value chain mapping workshop.
Frequently asked questions
Why is Scope 3 difficult to measure?
The emissions occur at suppliers and customers, outside your control. You rely on their data, which is often missing, estimated or inconsistent. Long value chains add layers of estimates, and many teams lack the people and tools to manage the data.
What percentage of companies measure Scope 3?
Few measure it fully. In the 2024 BCG and CO2 AI survey of nearly 2,000 companies, only 9% said they comprehensively report Scope 1, 2 and 3 emissions.
Can you use industry averages for Scope 3?
Yes. The GHG Protocol allows secondary data such as industry averages and spend-based factors, especially for screening and for smaller suppliers. You should disclose the methods used and replace averages with primary data where emissions are highest.
Do you need data from every supplier?
No. Most companies rank suppliers by emissions and collect primary data from those that make up the largest share. The rest can be estimated with secondary data, as long as the approach is documented.
How accurate does Scope 3 need to be?
Accurate enough to support decisions and pass assurance. Regulators and auditors look for complete coverage, a documented method and steady improvement in data quality, not perfect figures from day one.
Talk to us about your Scope 3 data
If your Scope 3 numbers are holding back a target or disclosure, contact our team.
