Use the ADEME Base Empreinte spend-based ratios (updated in March 2025 using the FIGARO model): take spending by supplier category and apply the ratio, in kgCO2e per €k. This is enough to identify the main categories and start. Then refine it using physical data for the 3 to 5 dominant categories.
Read the source article: Scope 3: definition, 15 categories and calculation method