Spend-Based Method
The spend-based method is a Scope 3 estimation technique that calculates emissions by multiplying procurement expenditure (in £ or $) by sector-level emission factors expressed as kgCO₂e per unit of currency. It is the most commonly used starting point for Scope 3 Category 1 (Purchased goods and services) when activity-level data is unavailable.
What is Spend-Based Method?
The spend-based method is the simplest and most widely used approach for estimating Scope 3 emissions from purchased goods and services (Category 1) and capital goods (Category 2). It uses environmentally extended input-output (EEIO) emission factors that express the average emissions intensity of economic sectors in terms of kgCO₂e per pound or dollar spent.
The calculation is straightforward: take the procurement spend in a given category (e.g., £500,000 on IT equipment), multiply by the EEIO emission factor for that sector (e.g., 0.28 kgCO₂e per £), and the result is the estimated emissions (140 tCO₂e). The factors are derived from national economic input-output tables combined with environmental satellite accounts that allocate emissions to each economic sector.
Commonly used EEIO datasets include: the DEFRA/DESNZ Scope 3 spend-based factors for the UK, the US EPA Supply Chain GHG Emission Factors, and academic databases like Exiobase. These factors are typically available at the level of broad economic sectors (e.g., "computer and electronic products," "food and beverage," "construction") and are updated periodically.
The spend-based method has clear advantages. It requires only financial data (procurement records, accounts payable), which most organisations already have. It covers the entire procurement portfolio without needing to engage individual suppliers. And it provides a rapid first estimate — a "screening" — of which Scope 3 categories and procurement areas are most material.
However, it has significant limitations. Spend-based factors are averages across entire economic sectors, so they cannot distinguish between a high-carbon supplier and a low-carbon one within the same sector. They are influenced by price — if the cost of a good increases due to inflation without any change in carbon intensity, the spend-based estimate rises. And they cannot capture the impact of supplier-specific decarbonisation actions. For these reasons, the spend-based method sits at the lower end of the GHG Protocol's data quality hierarchy. Organisations should treat it as a starting point and progressively replace spend-based estimates with activity-based or supplier-specific data for their most material categories.
Practical Examples
A professional services firm estimates its Scope 3 Category 1 by mapping its £12 million annual procurement spend across EEIO sectors — discovering that cloud hosting, office supplies, and catering are the three largest emission categories.
A manufacturer uses spend-based factors as a screening tool across all 15 Scope 3 categories, then focuses detailed data collection on the top three categories (purchased raw materials, freight, and packaging) that account for 80% of the spend-based total.
A university applies DEFRA spend-based factors to its procurement data, estimating total Scope 3 Category 1 at 8,500 tCO₂e from spend on construction, catering, IT, and laboratory supplies.
How Climatise Helps
Upload your procurement or accounts payable data and Climatise maps each spend line to the appropriate EEIO sector, applies the correct spend-based emission factor, and calculates Scope 3 Category 1 and 2 emissions automatically. The platform identifies your highest-impact spend categories so you know where to focus supplier engagement.
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