How to Calculate Scope 3 Emissions

Navigate the complexity of value chain emissions measurement across all 15 GHG Protocol categories.

In this guide

What Are Scope 3 Emissions?Step 1: Scope 3 Screening Step 2: Choose Your Calculation Method Step 3: Category-by-Category Calculation Step 4: Improve Data Quality Over Time

What Are Scope 3 Emissions?

Scope 3 emissions are all indirect emissions that occur in your organisation's value chain — both upstream (supply chain) and downstream (use of sold products, end of life). They typically represent the largest share of a company's total carbon footprint, often 70-90% or more.

Step 1: Scope 3 Screening

Start with a high-level screening to identify which of the 15 categories are relevant and material for your organisation.

Step 2: Choose Your Calculation Method

The GHG Protocol provides three main approaches: spend-based, average-data, and supplier-specific methods.

Step 3: Category-by-Category Calculation

Work through each material category using the appropriate method and DEFRA factors.

Step 4: Improve Data Quality Over Time

Scope 3 is a journey. Start with spend-based screening, then systematically improve data quality over successive years.

Key Takeaways

Scope 3 is typically 70-90% of total emissions for most companies

Start with spend-based screening, then improve data quality over time

Category 1 (purchased goods) is usually the largest source

Supplier engagement is key to moving from estimates to real data

Document your methodology — auditors expect transparency on assumptions

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Frequently Asked Questions

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