For many organisations, Scope 3 emissions represent the largest share of their carbon footprint often accounting for more than 70% of total greenhouse gas emissions. Yet they are also the most difficult emissions to measure.

Unlike Scope 1 and Scope 2 emissions, which originate from sources a business owns or directly controls, Scope 3 emissions occur throughout the wider value chain. They include emissions from suppliers, logistics providers, employees, customers and the end use of products and services.

This guide explains what Scope 3 emissions are, how they are calculated, the different calculation methods available, and practical steps organisations can take to improve the accuracy of their reporting.

What Are Scope 3 Emissions?

Scope 3 emissions are all indirect greenhouse gas emissions that occur across an organisation’s value chain but are not included within Scope 1 or Scope 2.

They are divided into:

• Upstream emissions – activities that occur before products or services reach your organisation.
• Downstream emissions – activities that occur after products or services leave your organisation.

The Greenhouse Gas Protocol identifies 15 categories of Scope 3 emissions, covering everything from purchased goods and employee commuting to product use and end-of-life disposal.

Why Is Scope 3 So Difficult to Measure?

Calculating Scope 3 emissions is challenging because organisations rarely control the activities that generate them.

Instead, businesses often rely on information from:

• Suppliers
• Manufacturers
• Freight companies
• Contractors
• Customers
• Waste management providers
• Industry databases

The quality and availability of this data can vary significantly, meaning organisations often begin with estimates before improving accuracy over time.

The Four Main Approaches to Calculating Scope 3 Emissions

There is no single calculation method suitable for every organisation. Most businesses use a combination of approaches depending on the availability of data.

1. Spend-Based Method

The spend-based method estimates emissions using the amount of money spent on goods or services.

Formula:

Emissions = Money Spent × Emission Factor

For example, if a business spends £100,000 on office furniture and the relevant emissions factor is 0.4 kg CO₂e per £1 spent:

100,000 × 0.4 = 40,000 kg CO₂e

This is often the easiest approach for organisations beginning their Scope 3 journey because financial data is readily available.

Advantages

• Simple to implement
• Uses existing accounting records
• Suitable for initial reporting

Limitations

• Less accurate
• Does not reflect supplier-specific performance
• May overestimate or underestimate emissions

2. Average Data Method

This approach estimates emissions using average industry emission factors based on quantities purchased.

For example:

• Kilograms of steel
• Tonnes of concrete
• Litres of fuel
• Kilograms of packaging

Formula:

Emissions = Quantity Purchased × Industry Emission Factor

This provides greater accuracy than spend-based calculations but still relies on average assumptions.

3. Supplier-Specific Method

Where available, organisations can obtain actual emissions data directly from suppliers.

Examples include:

• Product Carbon Footprints (PCFs)
• Environmental Product Declarations (EPDs)
• Verified supplier emissions reports
• Lifecycle assessment data

Because the calculation is based on actual supplier information, this is generally one of the most accurate approaches.

However, not all suppliers currently collect or publish this level of data.

4. Activity-Based Method

The activity-based method uses real operational information rather than averages.

Examples include:

• Distance travelled
• Fuel consumed
• Electricity used
• Kilograms transported
• Number of hotel nights
• Employee commuting distances
• Freight weights

Formula:

Emissions = Activity Data × Emission Factor

This approach often produces the most representative results where detailed operational information is available.

The 15 Scope 3 Categories

The Greenhouse Gas Protocol groups Scope 3 emissions into fifteen reporting categories.

Upstream

1. Purchased goods and services
2. Capital goods
3. Fuel and energy-related activities
4. Upstream transportation and distribution
5. Waste generated in operations
6. Business travel
7. Employee commuting
8. Upstream leased assets

Downstream

9. Downstream transportation and distribution
10. Processing of sold products
11. Use of sold products
12. End-of-life treatment of sold products
13. Downstream leased assets
14. Franchises
15. Investments

Not every category will apply to every organisation. Businesses should identify the categories that are relevant to their operations and prioritise those that contribute most significantly to their overall emissions.

Example: Calculating Scope 3 Emissions

Imagine a company purchases:

• £2 million of packaging
• £8 million of raw materials
• £500,000 of transport services
• £300,000 of business travel

Initially, the organisation may use spend-based emission factors to estimate emissions.

As reporting matures, the company could improve accuracy by:

• Collecting supplier-specific emissions data
• Measuring transport distances and vehicle types
• Recording actual business travel activity
• Calculating emissions for individual products

This gradual improvement is common and aligns with best practice in greenhouse gas reporting.

Data Sources for Scope 3 Calculations

Reliable Scope 3 reporting depends on high-quality data.

Common sources include:

• Procurement records
• Financial systems
• Supplier questionnaires
• Product carbon footprint studies
• Logistics providers
• Utility providers
• Employee travel records
• Waste contractors
• Environmental databases
• Lifecycle assessment software

Many organisations use a combination of internal operational data and recognised emissions factor databases to calculate their inventory.

Improving the Accuracy of Scope 3 Reporting

Most organisations do not achieve perfect Scope 3 reporting immediately. Instead, reporting typically develops over time.

A practical roadmap includes:

• Identifying relevant Scope 3 categories
• Prioritising the largest emission sources
• Improving supplier engagement
• Replacing estimated data with measured data
• Introducing digital monitoring systems
• Reviewing calculations annually
• Establishing clear governance and documentation

The objective should be continual improvement rather than perfection in the first reporting cycle.

The Future of Scope 3 Reporting

As sustainability expectations continue to evolve, businesses are moving towards more transparent and data-driven emissions reporting.

Advances in Digital Measurement, Reporting and Verification (D-MRV), Internet of Things (IoT) devices, satellite monitoring, artificial intelligence and blockchain-supported data integrity are making it easier to collect, verify and analyse environmental data across increasingly complex supply chains.

These technologies are expected to play a significant role in improving confidence in Scope 3 reporting and supporting more effective emissions reduction strategies.

How Kyoto Network Can Help

Calculating Scope 3 emissions can be complex, particularly for organisations with global supply chains or large numbers of suppliers.

Kyoto Network supports organisations by helping them:

• Identify material Scope 3 categories
• Develop robust carbon inventories
• Improve supplier engagement
• Collect and manage emissions data
• Build digital monitoring systems
• Strengthen ESG reporting
• Develop supply chain decarbonisation strategies

Kyoto Network has also developed the Supply Chain Emission Reduction Method (SCERM), an innovative framework designed to recognise and attribute measurable emissions reductions across supply chains. By combining digital monitoring, transparent reporting and practical implementation, SCERM helps organisations demonstrate real environmental impact while supporting broader sustainability objectives.

Frequently Asked Questions

Do all businesses need to calculate every Scope 3 category?

No. Organisations should identify which of the 15 categories are relevant to their operations and focus on those that are material to their overall emissions profile.

Which calculation method is the most accurate?

Supplier-specific and activity-based methods generally provide the highest level of accuracy because they use actual operational data rather than estimates.

Can Scope 3 emissions be estimated?

Yes. Many organisations begin with spend-based or average-data calculations before progressively improving data quality over time.

How often should Scope 3 emissions be calculated?

Most organisations calculate and report Scope 3 emissions annually, although many are moving towards more frequent monitoring as digital reporting systems become more advanced.

Final Thoughts

Calculating Scope 3 emissions is one of the most important—and most challenging—aspects of corporate sustainability reporting.

While no organisation starts with perfect data, businesses that establish a structured methodology, engage with suppliers and continuously improve data quality will gain a far better understanding of their environmental impact.

As expectations around ESG reporting, supply chain transparency and climate disclosures continue to grow, organisations that invest in accurate Scope 3 reporting today will be better positioned to reduce emissions, strengthen stakeholder confidence and build more resilient, sustainable supply chains.