Spend-Based Method
The spend-based method estimates greenhouse gas emissions by multiplying procurement expenditure (in dollars or other currency) by economic emission factors that represent the average emissions intensity per unit of spend in a given sector. It is the most accessible Scope 3 estimation approach but also the least precise.
The spend-based method uses Environmentally Extended Input-Output (EEIO) models — such as the US EPA's USEEIO or the European EXIOBASE — to estimate emissions from procurement data. These models map economic activity across hundreds of industry sectors to their average environmental impacts, producing emission factors in units like kg CO₂e per dollar spent.
The main advantage is accessibility: most organizations have procurement spend data by category, even if they lack physical activity data from suppliers. This makes spend-based the default starting point for Scope 3 Categories 1, 2, and parts of 4.
However, the method has significant limitations. It assumes industry-average emission intensity, which may not reflect specific suppliers' practices. It is sensitive to price fluctuations (inflation increases apparent emissions without any change in physical activity). And it cannot distinguish between a supplier who has invested in decarbonization and one who hasn't.
For these reasons, the GHG Protocol and SBTi recommend using spend-based methods as a starting point but progressively replacing them with activity-based or supplier-specific data. This transition is a key indicator of data maturity in corporate carbon accounting programs.
Frequently asked questions
What is the spend-based method in carbon accounting? +
The spend-based method estimates Scope 3 emissions by multiplying procurement spending by economic emission factors (from EEIO models like USEEIO or EXIOBASE). It is the most accessible approach but the least precise, as it assumes industry-average emission intensity.
When should you move beyond spend-based estimates? +
Organizations should progressively replace spend-based estimates with activity-based or supplier-specific data, starting with the highest-spending categories. The GHG Protocol and SBTi recommend this progression as a key indicator of data maturity.
Related terms
Scope 3 Emissions
Scope 3 emissions are all indirect greenhouse gas emissions that occur in an organization's value chain — both upstream (suppliers, purchased goods, business travel, employee commuting) and downstream (product use, end-of-life treatment, investments). Scope 3 typically represents 70–90% of a company's total carbon footprint.
Supply Chain Emissions
Supply chain emissions are the greenhouse gases produced throughout an organization's upstream and downstream value chain — from raw material extraction and manufacturing through distribution, product use, and end-of-life disposal. In GHG Protocol terms, these are Scope 3 emissions, and they typically represent the majority of a company's total footprint.
Emission Factor
An emission factor is a coefficient that converts an activity measurement — such as litres of fuel burned, kilowatt-hours of electricity consumed, or dollars spent on a commodity — into a quantity of greenhouse gas emissions, typically expressed in kilograms or tonnes of CO₂ equivalent (tCO₂e).
Carbon Accounting
Carbon accounting is the systematic process of measuring, recording, and reporting the greenhouse gas (GHG) emissions produced by an organization, product, or activity. It follows standardized methodologies — most commonly the GHG Protocol — to quantify emissions across Scope 1 (direct), Scope 2 (purchased energy), and Scope 3 (value chain) categories, producing an auditable inventory that underpins disclosure, reduction planning, and regulatory compliance.