Can I use spend data to calculate Business Travel emissions?
Yes, the GHG Protocol does allow the use of spend-based data to calculate Scope 3 emissions from business travel, but with some caveats.
How the GHG Protocol Handles This
The GHG Protocol’s Scope 3 Standard gives three main calculation methods for category 6 (“Business travel”):
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Distance-based method – Multiply passenger-kilometers by emission factors for travel modes.
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Fuel-based method – Use actual fuel consumed and emission factors.
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Spend-based method – Multiply the amount spent on travel services by an emission factor per unit of currency (e.g., kg CO₂e per $).
The spend-based method is explicitly recognized in the standard as an acceptable approach when better data (distance or fuel use) is not available. It is considered less accurate because spend doesn’t always correlate directly with distance traveled or efficiency — prices vary by route, class, season, and airline.
When Spend Data is Useful
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Early-stage inventories where detailed travel records aren’t available.
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Small companies that only have expense reports or credit card statements.
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Backfilling historic data before travel systems started tracking mileage.
Limitations to Be Aware Of
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Price ≠ Emissions: A first-class ticket costs more but may not scale proportionally in emissions.
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Currency-based emission factors need to be region- and year-specific to reflect differences in travel costs.
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Best Practice if Using Spend Data
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Trace uses spend based emission factors from EEIO (Environmentally Extended Input–Output) databases
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Trace separates emissions factors by travel type (air, rail, taxi, car hire, etc.) but separate factors are not available by class (e.g. economy, business class)
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Trace allows you to document the choice of method and assumptions for transparency.
- The GHG Protocol encourages shifting from spend- to activity-based methods as better data becomes available.