How to calculate your Scope 3 emissions: A practical guide for SMEs
Scope 3 emissions cover your entire value chain — and they're what your buyers are asking for. This guide walks you through the calculation methodology step by step.
Scope 3 emissions are all the indirect emissions in your value chain — both upstream (from your suppliers) and downstream (from your customers). For most companies, Scope 3 represents 70-90% of their total emissions footprint. And because SB 253, CSRD, and TCFD all require Scope 3 reporting, your buyers need your data.
The 15 Scope 3 categories
The GHG Protocol defines 15 Scope 3 categories. As a supplier, the most relevant are:
| Category | Description | Relevance |
|---|---|---|
| Cat 1: Purchased goods & services | Emissions from producing the goods and services you buy | High |
| Cat 3: Fuel & energy activities | Upstream emissions from producing the fuel and energy you use | Medium |
| Cat 4: Upstream transportation | Emissions from transporting goods to your facility | Medium |
| Cat 5: Waste | Emissions from disposing of waste generated in your operations | Low |
| Cat 6: Business travel | Emissions from employee business travel | Low-Medium |
| Cat 7: Employee commuting | Emissions from employees commuting to work | Low |
| Cat 11: Use of sold products | Emissions from customers using your products | High (if applicable) |
| Cat 12: End-of-life treatment | Emissions from disposing of your products | Medium |
Calculation methods
The GHG Protocol provides three main methods for calculating Scope 3 emissions:
Spend-based method
Multiply your spend on a category by an emission factor ($/tCO2e). The least accurate but easiest to calculate. Good for initial estimates.
Average-data method
Use industry-average emission factors for specific goods or services. More accurate than spend-based. Requires knowledge of what you're buying.
Supplier-specific method
Use actual emissions data from your suppliers. The most accurate method. Requires your suppliers to provide their Scope 1 and 2 data.
Further reading
📊 GHG Protocol Scope 1, 2 & 3 explained →Related articles
SB 253: What every supplier to US companies needs to know in 2025
California's Climate Corporate Data Accountability Act is reshaping what large US companies must report — and that means asking their suppliers for emissions data.
TCFD reporting for UK SMEs: what your buyers will ask for
The TCFD framework is now mandatory for large UK companies. If you supply them, they will ask you for climate data. Here is what to prepare.
CSRD for non-EU suppliers: what UK SMEs need to provide
The EU's CSRD does not apply directly to UK companies — but if you supply large EU businesses, they will ask you for sustainability data.
Free Scope 3 calculation template
Download our Scope 3 calculation spreadsheet with pre-loaded DEFRA emission factors.