Short answer: if a customer asks your company for Scope 1, Scope 2, and Scope 3 emissions, they are usually asking for a structured greenhouse gas response, not a broad sustainability essay. Scope 1 covers direct emissions from sources your company owns or controls. Scope 2 covers purchased electricity, steam, heat, or cooling. Scope 3 covers other value-chain emissions, such as purchased goods, logistics, travel, waste, and use of sold products. As a supplier, the practical job is to confirm exactly which scopes the customer is asking for, collect the right activity data, document assumptions, and send back numbers with enough methodology and evidence to be understood.
A supplier emissions request often lands with the person closest to the customer, not the person closest to the data. An account manager receives a portal reminder. Finance is asked for invoices. Operations is asked for fuel use. HR is asked for employee commuting or travel. Nobody is quite sure whether the buyer wants a full company footprint, a partial Scope 1 and 2 response, a specific Scope 3 category, or emissions connected to a product or service.
That is why the first step is not calculation. The first step is interpretation. Before building a spreadsheet, preserve the original request wording, deadline, reporting year, customer name, portal instructions, requested scopes, and any required methodology or evidence. If the request is unclear, ask for clarification before creating numbers that may not answer the actual question.
Why Scope 1, 2, and 3 feel different for suppliers
In a corporate sustainability report, Scope 1, 2, and 3 are often presented as a company-wide inventory. In a supplier request, the same scopes are used for a more urgent purpose: a customer is trying to understand emissions in its own value chain.
That changes the practical question. The buyer may need your company-level emissions because your business is part of their purchased goods and services, logistics, outsourced services, technology, marketing, facilities, professional services, or manufacturing supply chain. They may also need enough detail to replace estimates with supplier-specific data, answer CDP or EcoVadis questions, meet internal procurement requirements, or support their own Scope 3 reporting.
The GHG Protocol Corporate Standard is the usual foundation for company-level GHG inventories. CDP also aligns its climate reporting requirements with the GHG Protocol Corporate Standard, Scope 2 Guidance, and Scope 3 Standard. That does not mean every supplier request is identical, but it does mean the scopes have a common accounting language.
Scope 1 emissions: direct emissions you own or control
Scope 1 emissions come from sources your company owns or controls. For many suppliers, this includes fuel burned in boilers, generators, furnaces, kitchens, production equipment, company vehicles, and on-site processes. It can also include fugitive emissions, such as refrigerant leakage from air-conditioning or cooling systems.
The evidence is usually operational: fuel invoices, meter readings, vehicle fuel records, maintenance logs, refrigerant service records, equipment lists, and site-level activity data. The calculation usually converts activity data, such as liters of diesel or kilograms of refrigerant, into CO2e using appropriate emission factors.
If your company has no owned vehicles, no on-site fuel use, and no relevant process or refrigerant emissions, Scope 1 may be small or zero. But do not assume that before checking facilities, operations, and finance records.
Scope 2 emissions: purchased energy
Scope 2 emissions cover purchased or acquired electricity, steam, heat, and cooling. For many office-based or service suppliers, Scope 2 is the first material category because electricity is visible in utility bills and landlord recharge statements.
Scope 2 often needs two kinds of care. First, collect the activity data: kWh by site, reporting period, entity, and meter if available. Second, understand whether the customer expects location-based figures, market-based figures, or both. The GHG Protocol Scope 2 Guidance introduced requirements for accounting for energy contracts and instruments, including renewable energy certificates, and for transparent disclosure of energy purchases.
If your office is leased and electricity is included in rent, use the best available evidence. That might be landlord data, sub-meter readings, floor-area allocation, headcount allocation, or another reasonable estimate. Label the method honestly. A clear assumption is much better than a number with no explanation.
Scope 3 emissions: value-chain emissions
Scope 3 is where supplier reporting usually becomes messy. The GHG Protocol Scope 3 Standard covers 15 upstream and downstream categories, and it is designed to help companies assess value-chain emissions and engage suppliers and customers. For suppliers, the customer may ask for all relevant Scope 3 categories, or only the categories most connected to the service being provided.
Common supplier categories include purchased goods and services, capital goods, fuel- and energy-related activities, upstream transport, waste, business travel, employee commuting, leased assets, downstream transport, use of sold products, and end-of-life treatment. Not every category applies to every company. A software consultancy, outsourced marketing provider, logistics supplier, manufacturer, and office services firm will have different Scope 3 profiles.
Scope 3 data can come from spend, supplier-specific data, travel records, freight records, waste reports, procurement records, activity quantities, product data, or estimates. The key is to state what you used and why. If you used spend-based estimates because supplier-specific data was unavailable, say that. If you excluded a category because it was not relevant, explain the basis.
What a customer-ready response should include
A useful supplier response is not just a table of numbers. It should make the response understandable to the buyer. At minimum, prepare:
- the reporting period and organizational boundary;
- Scope 1, Scope 2, and requested Scope 3 results in CO2e;
- the source data used for each material category;
- the emission factor sources and versions;
- the assumptions and estimates used where direct data was unavailable;
- any exclusions, with reasons;
- supporting evidence such as invoices, utility data, travel reports, or fuel records; and
- a short methodology note that explains how the numbers were produced.
If the customer has sent a portal or questionnaire, map your response to the fields in that portal. If they have asked for a file, create a small evidence pack. If the request names a service, product, contract, or Microsoft-style service-level accounting requirement, a company-level inventory may not be enough. You may need service-level GHG accounting as well.
Common mistakes suppliers make
The most common mistake is answering too quickly. A team sees "Scope 1, 2, and 3" and immediately starts building a full ESG project. That can waste time if the customer only needs a scoped emissions response.
Another mistake is skipping the methodology. Numbers without boundaries, factors, assumptions, and evidence are hard for a customer to reuse. A third mistake is treating Scope 3 as optional because the data is imperfect. Scope 3 often needs estimates at first, but the response should still explain what was estimated and how it can improve next year.
Finally, do not call a calculation "verified" or "assured" unless an independent assurance or verification engagement has actually been performed. A consultant can help calculate and document the inventory, but that is different from independent assurance.
Where to start
If you are responding to a customer request, start with the actual request wording. Then use a practical collection file like the Supplier GHG Reporting Checklist. If the request is still unclear, Keslio's supplier request support can help interpret the request and define the response path. If you already know you need the calculations, Keslio's GHG emissions calculations support can help build the inventory, methodology note, and evidence trail.
Source notes
This article is grounded in the GHG Protocol Corporate Standard, Scope 2 Guidance, Scope 3 Standard, and CDP's stated alignment with GHG Protocol reporting requirements.
