Scope 1, 2 and 3 Emissions Explained: How to Calculate Each

What are Scopes 1, 2 and 3?

The GHG Protocol Corporate Standard is the most widely used framework for corporate greenhouse gas accounting. It sorts a company's emissions into three scopes, which show where the footprint comes from and where to act to reduce it.

The scopes are the common language of carbon reporting: the EU's CSRD and CBAM, ISSB-based disclosures and SBTi targets all build on them.

Scope 1: direct emissions

Scope 1 covers emissions from sources the company owns or controls: fuel burned in boilers, furnaces and company vehicles; fugitive emissions such as refrigerant leaks; and process emissions such as calcination in cement or iron ore reduction in steelmaking.

To calculate Scope 1 you need fuel consumption by type (diesel, natural gas, LPG, coal), refrigerant top-ups by gas, and production data for process emissions. Each activity is multiplied by an emission factor from a recognised source (see where to find them below).

Scope 2: purchased energy

Scope 2 covers emissions from generating the electricity, steam, heat or cooling a company buys and consumes. Grid emission factors vary by country and region and change with the generation mix.

The GHG Protocol's Scope 2 Guidance asks companies to report two figures: location-based, using average grid factors, and market-based, reflecting contractual instruments such as renewable energy certificates and power purchase agreements. Companies that buy renewable electricity through these instruments usually report a lower market-based figure.

Scope 3: value chain emissions

Scope 3 covers all other indirect emissions in the value chain, in 15 categories: 8 upstream, such as purchased goods and services, and 7 downstream, such as the use of sold products. According to the GHG Protocol, Scope 3 is the largest share of emissions for many companies, although in energy-intensive sectors such as cement and steel, Scope 1 usually weighs more.

In heavy industry, the categories that matter most are usually Category 1 (purchased goods and services), Category 4 (upstream transportation and distribution), Category 9 (downstream transportation and distribution) and Category 11 (use of sold products). For banks and investors, Category 15 (investments) tends to dominate.

Scope 3 calculations combine supplier-specific data, average data and spend-based estimates where primary data is missing. Your report should state which categories are included, which methods were used and why any category was left out.

Where to find emission factors in Ireland

The Sustainable Energy Authority of Ireland (SEAI) publishes emission factors for fuels and for grid electricity, and the EPA compiles Ireland's national greenhouse gas inventory. Record the source, version and year of every factor, because factors are updated as the fuel and grid mix changes.

Common mistakes

• Using outdated factors, or factors from the wrong country or grid.
• Leaving out fugitive emissions, such as refrigerant leaks.
• Reporting a single Scope 2 figure when you hold renewable energy contracts.
• Extrapolating one supplier's data to the whole value chain without adjustment.
• Building the inventory once a year in spreadsheets, months after the fact, when the data could guide operating decisions.

How CarbonOS automates the inventory

Carbonova CarbonOS connects ERP, SCADA, IoT and meter data through Signal Ingest, calculates emissions with versioned emission factors through the emissions calculation API and keeps the inventory current with Carbon Intelligence, including anomaly detection and the data lineage behind each figure for your auditors.

To see a Scope 1, 2 and 3 inventory built from your own data, book a demo.

What is the difference between Scope 1 and Scope 2?

Scope 1 is direct emissions from sources you own or control, such as boilers, furnaces, company vehicles and industrial processes. Scope 2 is indirect emissions from generating the energy you buy, such as grid electricity. Diesel burned in your own lorries is Scope 1; the electricity on your energy bill is Scope 2.

What goes into a Scope 3 emissions report?

Indirect emissions across the value chain, organised in the GHG Protocol's 15 categories. A good report states which categories are relevant, which calculation methods were used (supplier-specific, average-data or spend-based) and why any category was excluded.

How often should emission factors be updated?

At least every reporting year, since publishers release new factors annually. Record the source, version and year of each factor so an auditor can reproduce every figure.

Last reviewed: 22 October 2026