Your own sites, fuels and electricity are only part of your carbon footprint. For most companies, the larger part comes from what they buy and from what happens to their products after sale. The GHG Protocol puts these emissions in Scope 3 and splits them into 15 categories. Each category needs its own data and its own method.
Scope 3 emissions: indirect emissions in your value chain, from sources that your company does not own or control.
Upstream, categories 1 to 8: emissions linked to what you buy, such as goods, capital goods, transport and business travel.
Downstream, categories 9 to 15: emissions linked to what you sell, such as transport, product use and end of life.
First step: a screening that shows which categories matter most for your company.
Before you calculate all 15 categories, start with a screening. It shows which categories really drive your result. The GHG Protocol does not ask you to calculate each category with the same accuracy. In practice, a few categories usually make up most of Scope 3, and the rest is small. We describe the screening step by step in Scope 3 screening: how to find the categories that matter.
For a first estimate, you do not need supplier data. The simplest method is the spend-based method. You multiply spend from your accounts by emission factors for each group of purchases, for example from the USEEIO or EXIOBASE databases. It works well for categories 1, 2, 4 and 6. It shows quickly where your emissions are. Then you replace the estimates with better data, step by step. You find the details and a worked example in the spend-based method for Scope 3.
The 15 Scope 3 categories fall into two groups:
Upstream emissions: emissions linked to the costs of your company, that is, to what you buy.
Downstream emissions: emissions linked to the revenue of your company, that is, to what you sell.
Scope 1 covers direct emissions from sources that your company owns or controls: fuel burnt in boilers and furnaces, your vehicle fleet and refrigerant leaks. Scope 2 covers emissions from the production of the energy you buy: electricity, heat, steam and cooling. Scope 3 covers everything else. These are indirect emissions in your value chain, outside your direct control. They happen at suppliers, in transport, and in the use and disposal of the products you sell.
The practical difference: you calculate Scopes 1 and 2 from your own meters and invoices. For Scope 3, you need data from business partners, or an estimate.
Is Scope 3 mandatory?+
It depends on what applies to your company. There are four sources of the obligation, and each works on its own:
GHG Protocol (Corporate Standard): it requires Scopes 1 and 2. Scope 3 is voluntary under this standard.
CSRD and ESRS E1: Scope 3 emissions are a mandatory disclosure in requirement E1-6. Since the Omnibus I package of 2026, the CSRD covers far fewer companies. It applies to EU companies with more than 1,000 employees and more than EUR 450 million net turnover. Companies with up to 750 employees may leave out Scope 3 in the first year of their report.
SBTi: under the current criteria, you need a Scope 3 target when Scope 3 is more than 40% of your total emissions. The Corporate Net-Zero Standard V2.0 changes this rule for new submissions from 2027.
Market demands: in practice, the most common reason. Customers ask questions, tenders set criteria, and EcoVadis and CDP send questionnaires. There are no size thresholds here: what counts is what your customer asks for.
Status: October 2026. The scope and dates of the CSRD changed several times in recent years, so check the current rules before you report.
For which companies does Scope 3 matter most?+
It matters most where value is created outside your own walls. In production and processing, category 1 (purchased goods and services) usually leads. In trade, distribution and e-commerce, category 1 adds to transport in categories 4 and 9. Some companies make products that use energy, such as appliances, electronics, machines and vehicles. For them, category 11 (use of sold products) can be larger than all the others together.
Construction and property development also belong here (building materials and the life cycle of buildings). So do financial institutions, where category 15 (investments) is usually most of the footprint, and franchisors (category 14).
A simple rule: if your company buys and sells more than it makes itself, Scope 3 will be the largest part of its footprint.
You can see this in our projects. A corporate group got a full Scope 3, with 15 categories in a yearly calculator. For a manufacturer, the largest impact came only after the sale of the product (category 11). For a service company without large production, purchases and employee commuting were the main sources of emissions. An automotive component maker built its footprint in stages: first Scopes 1 and 2, then a Scope 3 method.
For which companies is Scope 3 not relevant?+
Almost no company has zero Scope 3, because every company buys something. But single categories can be irrelevant, not the whole of Scope 3.
A service company with no fleet and no physical products has no categories 9 to 13. Without leasing, you have no categories 8 and 13. Without franchises, you have no category 14, and without shares in other companies, no category 15. Energy-intensive production with its own energy source has larger Scopes 1 and 2, but category 1 usually still matters.
The GHG Protocol lets you leave out a category that is not relevant. But you must explain this decision in your report. It is not enough to leave it out without a word. We describe how to do this assessment in our article on Scope 3 screening.
Do you need to calculate all 15 categories?+
No. You need to review and assess all of them, and calculate the relevant ones. Some categories do not exist in your company at all.
The usual relevance criteria are the estimated share of emissions and the effect on the decisions of report users. Business and regulatory risk, your influence on suppliers and the availability of data also count. You describe the decision and its basis in the report.
Can you use different methods to calculate Scope 3?+
Yes, and this is normal practice. The GHG Protocol allows you to mix methods between categories and also within one category.
Three methods are the most common. The spend-based method multiplies spend by a factor per unit of currency; it is the fastest and the least accurate. The average-data method, also called activity-based, multiplies physical amounts (kilograms, tonnes, kWh, tonne-kilometres) by average factors. The supplier-specific method uses data from a specific supplier; it is the most accurate and the preferred one.
A typical path: start with the spend-based method for everything to see where emissions are. Then use a more accurate method where the largest items are: for key suppliers and main raw materials.
One condition: describe the method and the source of factors for each category. If you change the method between years, show it as a change of method. After a significant change, you must recalculate the base year.
Where do you get emission factors for Scope 3?+
There are four sources, from the least to the most accurate. First, input-output (financial) databases: USEEIO from the US EPA in kg CO₂e per USD, and EXIOBASE in kg CO₂e per EUR. Both are free and suit the spend-based method. Second, process and government databases: the UK Government GHG Conversion Factors for transport, waste, fuels and hotel stays. National factors for grid electricity, and the IEA and AIB for energy mixes, belong here too. Third, commercial LCA databases: ecoinvent, Sphera and Idemat; they are paid and cover the most materials. Finally, supplier data: EPDs, product carbon footprints under ISO 14067 and answers to questionnaires.
Three things often go wrong. First, the year and currency of the factor: you must adjust financial factors for inflation and exchange rates. Second, factors with a different scope: some include upstream fuel emissions and some do not, and you must not mix them. Third, a missing source: without a documented source and year for each item, the report will not pass verification.
What share of a company's carbon footprint is usually Scope 3?+
In most industries, Scope 3 is the largest part of the footprint, usually many times larger than Scopes 1 and 2 together. The exact share depends on the business model: the more a company buys and sells compared with what it makes itself, the higher the share.
The practical result: a decarbonisation strategy based only on Scopes 1 and 2 usually covers a minority of the company's emissions.
Are one company's Scope 3 emissions another company's Scopes 1 and 2? Is this double counting?+
Yes, these are the same emissions seen from two sides, and this is intended. Scope 3 is not for adding up emissions across the economy. It shows a company where emissions happen in its value chain and where it can act to reduce them.
So you must not add up Scopes 1, 2 and 3 of many companies: the result would be many times too high. Within one organisation, the GHG Protocol makes sure that the same emission is not counted twice. What is in Scope 1 or 2 cannot also be in Scope 3. This is why category 3, for example, covers only fuel- and energy-related emissions that are not in Scopes 1 and 2.
What data do you need to calculate Scope 3?+
Start with the data your company already has. From accounting: purchases by cost category (for the spend-based method), fixed assets, and the costs of transport and business travel. From operations: physical amounts, such as raw materials used, tonne-kilometres of transport, and the mass and treatment of waste. From HR: employee commuting (usually a survey) and travel expense reports. From suppliers: product emission factors, EPDs and carbon footprint statements for the main items. From sales: volumes, energy use and the lifetime of products, which you need for categories 10 to 12.
For each item, add the data year, the unit and the source of the factor. In practice, the largest part of the work is not the calculation. It is putting the data into one structure that you can repeat next year and defend in front of a verifier.
