Scope 3 Emissions Explained: Where to Start When Data is Scarce
Scope 3 emissions typically represent 70–90% of a company's carbon footprint — yet they're the hardest to measure. This guide gives you a practical starting point.
What is Scope 3?
Under the GHG Protocol Corporate Standard, greenhouse gas emissions are divided into three scopes:
Scope 1
Direct emissions from sources owned or controlled by the company (e.g., company vehicles, boilers, process emissions).
Scope 2
Indirect emissions from the generation of purchased energy (electricity, heat, steam).
Scope 3
All other indirect emissions that occur in the value chain — upstream (suppliers) and downstream (customers and product use).
The 15 Scope 3 Categories
The GHG Protocol divides Scope 3 into 15 categories across upstream and downstream activities:
| Cat | Category | Typical % of Footprint |
|---|---|---|
| 1 | Purchased goods & services | High (often 40–70%) |
| 2 | Capital goods | Variable |
| 3 | Fuel & energy activities | Low–Medium |
| 4 | Upstream transport & distribution | Low–Medium |
| 5 | Waste generated in operations | Low |
| 6 | Business travel | Low–Medium |
| 7 | Employee commuting | Low |
| 8 | Upstream leased assets | Variable |
| 9 | Downstream transport & distribution | Medium |
| 10 | Processing of sold products | Variable |
| 11 | Use of sold products | High (for consumer goods, energy products) |
| 12 | End-of-life treatment | Low |
| 13 | Downstream leased assets | Variable |
| 14 | Franchises | Variable |
| 15 | Investments | High (for financial institutions) |
Step 1: Screen and Prioritise
Don't try to measure everything at once. Start with a hotspot screening to identify which categories are likely to be most significant for your industry:
- Use industry benchmarks or sector averages to estimate relative magnitude
- Focus on categories that are clearly material and where you have some data
- Categories 1 (purchased goods), 11 (product use), and 15 (investments) are often the largest
- GHG Protocol guidance lists which categories are likely most relevant for your sector
Step 2: Choose Your Calculation Method
For each category, three main methods are available:
Spend-based
Multiply spend (£) by spend-based emission factors. Best for early-stage estimates where supplier data is limited.
Easiest to implementActivity-based
Use physical activity data (kg, kWh, km) with specific emission factors. More accurate than spend-based.
Preferred methodSupplier-specific
Use actual emissions data provided directly by suppliers. Most accurate but requires supplier engagement.
Gold standardStep 3: Collect Data and Calculate
For your first Scope 3 inventory, focus on getting estimates rather than perfect data. A spend-based approach for Category 1 can be done with your accounts payable data and publicly available emission factor databases:
- Defra GHG Conversion Factors — UK Government, updated annually (free)
- EPA Supply Chain Emission Factors — US spend-based factors (free)
- Exiobase / EEIO — academic-grade input-output emission factors
Common Mistakes to Avoid
- Omitting categories without justification — document why each category is or isn't included
- Using outdated emission factors — always use the most recent year's factors
- Double-counting — e.g., including both upstream transport and purchased goods emissions for the same activity
- Ignoring data quality — score your data quality and report uncertainty
Ready to calculate your Scope 3 emissions?
Our Scope 3 Value Chain Emissions Calculator covers all 15 categories with built-in emission factors and methodology guidance.