Activity-Based Method
The activity-based method calculates Scope 3 emissions using real physical activity data — such as kilometres travelled, kilowatt-hours consumed, tonnes of material purchased, or nights in hotels — combined with specific emission factors for each activity. It is more accurate than spend-based estimation.
What is Activity-Based Method?
The activity-based method is a Scope 3 calculation approach that uses physical measures of activity — rather than financial spend — as the input for emissions calculation. It sits in the middle of the GHG Protocol's data quality hierarchy, above spend-based estimation and below supplier-specific data.
Instead of multiplying pounds spent by a sector-average financial emission factor, the activity-based method multiplies a physical quantity (km, kWh, kg, litres, nights, passenger-km) by a published emission factor for that specific activity. For example: 100,000 km of domestic flights × DEFRA emission factor per passenger-km = business travel emissions. Or: 50 tonnes of steel purchased × lifecycle emission factor per tonne of steel = purchased goods emissions.
Activity-based data is more accurate than spend-based for several reasons. It is not distorted by price fluctuations (paying more for the same flight does not change the emissions). It is more granular (short-haul vs. long-haul economy vs. business class have different per-km factors). And it reflects the actual physical scale of the activity rather than a financial proxy.
The DEFRA emission factor dataset provides activity-based factors for many Scope 3 categories: business travel (per passenger-km by flight class and distance band, per vehicle-km by car type, per km by rail), hotel stays (per night by country), freight transport (per tonne-km by mode), waste disposal (per tonne by type and disposal route), and water (per cubic metre). For purchased goods, lifecycle assessment (LCA) databases such as ecoinvent provide emission factors per unit of material or product.
The main limitation of the activity-based method is data availability. Collecting physical activity data requires systems and processes: travel booking platforms that track distance, procurement systems that record material quantities, waste management contracts that report tonnage by type. Many organisations collect activity data for some categories (e.g., travel and waste are relatively easy) while relying on spend-based estimates for others (e.g., purchased goods with complex supply chains).
Practical Examples
A consultancy calculates business travel emissions using the activity-based method: 2 million passenger-km of domestic flights (DEFRA factor per km by class), 500,000 km of rail travel, and 3,000 hotel nights (DEFRA factor per night) — all using physical activity data rather than spend.
A food manufacturer estimates emissions from purchased packaging using activity data: 2,000 tonnes of corrugated cardboard × lifecycle emission factor per tonne, plus 500 tonnes of plastic film × per-tonne factor — yielding a more accurate figure than the spend-based alternative.
A logistics company calculates upstream freight emissions using tonne-km data from its carriers: 5 million tonne-km by road and 2 million tonne-km by rail, each multiplied by the DEFRA freight emission factor for that mode.
How Climatise Helps
Climatise supports activity-based calculations across all Scope 3 categories — from travel distances and hotel nights to material tonnages and waste volumes. Upload activity data in any format and the platform matches each entry to the correct emission factor, producing higher-accuracy Scope 3 figures than spend-based estimates alone.
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