Activity-based data means measuring emissions from real-world consumption — kilowatt-hours (kWh) of electricity, litres of fuel, kilometres travelled, kilogrammes of material purchased, tonnes of waste disposed. These physical units are then multiplied by an appropriate emission factor to give a result in tCO₂e.
It is the opposite of spend-based estimation, which infers emissions from how much money was spent on a category of goods or services.
Why it matters
Activity-based data is materially more accurate — often by an order of magnitude. Two suppliers selling the same product at very different prices will produce broadly similar emissions per unit, but a spend-based calculation would treat the more expensive one as far more carbon-intensive. That is why the GHG Protocol's data quality hierarchy ranks activity-based methods above spend-based methods, and why credible reporting frameworks reward activity-based reporting.
It is also defensible. An auditor or procurement reviewer can trace activity data back to a meter reading, a fuel receipt, or a weighbridge ticket. Spend data, by contrast, reflects pricing as much as physical reality.
A practical example
If a manufacturer wants to calculate emissions from purchased steel, the activity-based approach uses tonnes of steel purchased × the relevant emission factor (kgCO₂e/kg). The spend-based approach would multiply pounds spent on steel × an industry-average emission factor (kgCO₂e/£). The first reflects what was actually bought; the second reflects what was paid.
Every Carbon Stamp engagement prioritises activity-based data wherever possible — this is the core of our data collection methodology.