How to Calculate Scope 3 Emissions: A Practical Beginner’s Guide

How to Calculate Scope 3 Emissions: A Practical Beginner’s Guide

Scope 3 emissions are the indirect greenhouse gas emissions that occur across a company’s value chain. They do not come directly from sources the company owns or controls, and they are not simply purchased electricity or heat. Instead, Scope 3 covers emissions linked to suppliers, transport, business travel, product use, waste, investments, and other upstream or downstream activities.

The GHG Protocol Corporate Value Chain, or Scope 3 Standard, provides a global methodology for companies to account for and report Scope 3 emissions across sectors. It is supported by Scope 3 Calculation Guidance, which gives methods, data sources, and worked examples for the 15 Scope 3 categories.

Step 1: Understand the 15 Scope 3 Categories

Before calculating anything, a company needs to understand what activities may fall under Scope 3. The GHG Protocol divides Scope 3 emissions into 15 categories, including purchased goods and services, capital goods, fuel- and energy-related activities, transportation, waste, business travel, employee commuting, leased assets, use of sold products, end-of-life treatment, franchises, and investments.

For beginners, the easiest way to think about it is this: upstream emissions happen before the company sells its product or service, while downstream emissions happen after the sale.

A clothing company, for example, may have upstream emissions from cotton farming, fabric production, packaging, and shipping. It may have downstream emissions from customers washing clothes and disposing of garments.

Step 2: Decide Which Categories Are Relevant How to Calculate Scope 3 Emissions

A company does not calculate Scope 3 properly by guessing. It first identifies which categories are relevant to its business model. A software company, a bank, a car manufacturer, and a food company will not have the same Scope 3 profile.

For example, a bank may focus heavily on Category 15, investments. A car manufacturer may focus on purchased materials and the use of sold products. A retailer may focus on purchased goods, transportation, and product end-of-life.

IFRS S2 also refers to the 15 Scope 3 categories in the GHG Protocol Corporate Value Chain Standard and says companies should consider the entire value chain, upstream and downstream, when disclosing Scope 3 greenhouse gas emissions.

Step 3: Collect Activity Data

The next step is collecting activity data. Activity data is the real-world information used to estimate emissions.

Examples include:

• kilograms of purchased materials,

• kilometres travelled,

• litres of fuel used by transport providers,

• amount spent on goods or services,

• tonnes of waste generated,

• number of hotel nights,

• units of products sold,or financial exposure to investments.

The quality of the calculation depends heavily on the quality of the data. Supplier-specific data is usually better than broad industry averages, but it is not always available. That is why companies often start with estimates and improve data quality over time.

Step 4: Choose the Calculation Method

The basic logic of many Scope 3 calculations is simple:

Activity data × emission factor = greenhouse gas emissions

An emission factor converts an activity into estimated emissions. For example, if a company knows the distance goods travelled by truck, it can apply a transport emission factor. If it knows how much of a material it purchased, it can apply a material-related emission factor.

The GHG Protocol Scope 3 Calculation Guidance provides different methods for different categories, including supplier-specific, average-data, spend-based, distance-based, fuel-based, waste-type-specific, and use-phase methods.

Step 5: Convert Results Into CO₂e

Greenhouse gas emissions are usually reported in carbon dioxide equivalent, or CO₂e. This allows different greenhouse gases to be expressed using one common unit. For example, methane and nitrous oxide have different warming effects, so CO₂e helps make the results easier to compare.

A company should document the greenhouse gases included, the emission factors used, the data sources, and any assumptions made.

Step 6: Avoid Double Counting Confusion

Scope 3 can create confusion because one company’s Scope 3 emissions may be another company’s Scope 1 emissions. For example, emissions from a supplier’s factory may be Scope 1 for the supplier but Scope 3 for the company buying the product.

This does not mean the calculation is wrong. It means the same real-world emissions can appear in different companies’ inventories from different perspectives.

Step 7: Pay Special Attention to Financed Emissions

For financial institutions, investments can be one of the most important Scope 3 categories. IFRS S2 includes requirements around Scope 3 greenhouse gas emissions, and the ISSB issued targeted amendments in December 2025 to support implementation, including clarification related to Scope 3 Category 15 financed emissions.

This is important because banks, insurers, and asset managers may have relatively small operational emissions but large climate exposure through lending and investment portfolios.

Step 8: Improve the Calculation Over Time

Scope 3 calculation is not usually perfect in the first year. Companies may begin with estimates, then improve supplier engagement, collect better primary data, refine emission factors, and strengthen internal controls.

The GHG Protocol is also revising its Scope 3 Standard, and its March 2026 progress update confirms that the revision process is ongoing.  This means companies should follow official updates while continuing to improve their current reporting practices.

Conclusion

Calculating Scope 3 emissions is difficult, but the process becomes easier when broken into steps: identify the relevant categories, collect activity data, choose the right method, apply emission factors, convert results into CO₂e, document assumptions, and improve data quality over time.

In simple terms: Scope 3 calculation is about tracing emissions beyond the company’s walls and turning value-chain activity into measurable climate data.