Spend-based carbon accounting

Spend-based carbon accounting estimates emissions based on actual spending on goods and services. The method converts monetary amounts (in EUR, USD, etc.) into emissions using established conversion factors. It gives an overview of which emissions are linked to financial spending on different products and services.

A manufacturer that buys raw materials can use spend-based accounting to estimate emissions by converting steel spending into a carbon footprint. If the company spends $100,000 on steel and the emission factor is 1.5 kg CO₂e per dollar, that gives an estimated 150,000 kg CO₂e.

  1. Simplicity and speed: requires less granular data and can be deployed quickly.
  2. Broad applicability: useful early on for organisations with diverse, complex supply chains, where detailed data is hard to obtain.
  1. Lower accuracy: estimates are often imprecise — due to generalised conversion factors and effects like inflation.
  2. Over-generalisation: specific practices or efficiencies of individual suppliers aren’t captured.
  3. Limited insights: spend-based data alone makes it hard to build a robust decarbonisation roadmap.

Activity-based carbon accounting

Activity-based carbon accounting calculates emissions from concrete activities or processes inside the company. Emissions are quantified directly from measurable activities — kilometres driven, kilograms or litres bought, kilowatt-hours consumed. The method delivers detailed operational insights and enables targeted emissions reductions.

A logistics company can use activity-based accounting to measure emissions from its vehicle fleet. Using kilometres driven or litres of fuel consumed and the respective vehicle type, emissions per trip can be calculated. If a 3.5-t truck at 100% load drives 10,000 km and consumes 5,000 litres of diesel, emissions can be calculated precisely with the known emission factor in kgCO₂e or tCO₂e per litre.

  1. Granular insights: detailed data on concrete activities enables targeted measures.
  2. Operational efficiency: helps identify and implement process improvements.
  1. Complexity: requires detailed data collection and analysis per activity.
  2. Resource-intensive: can be time-consuming — especially for emission sources that are hard to automate.

Real-world examples across sectors

  1. Retail: a wholesaler using spend-based accounting estimates emissions across total spending in different product categories. A switch to activity-based accounting may reveal that transport and logistics are the biggest emissions drivers — enabling route optimisation and footprint reduction.
  2. Tech: a tech company initially uses spend-based accounting to estimate emissions from buying electronic components. Switching to activity-based accounting makes visible that data centre operations are a significant emission source — and that targeted investment into energy-efficient technologies pays off.
  3. Agriculture: an agribusiness estimates emissions from buying fertilisers and seeds with spend-based accounting. Activity-based accounting can show that specific practices like irrigation and pesticide use are the main emission sources — providing the basis for better management.

Bottom line

Both methods have their place in a comprehensive carbon-management strategy. Spend-based delivers a fast, broad overview. Activity-based delivers the level of detail needed for precise emissions tracking and targeted reduction. Companies should review their concrete needs, data availability and sustainability goals when choosing the right method per emission source.

Anyone who understands and applies these methods effectively makes better-informed decisions — improving environmental performance while strengthening reputation and competitiveness in an increasingly eco-conscious market.