# How do I work out precursor emissions when I buy the same steel from several suppliers?

Canonical: https://senseible.earth/answers/cbam-precursor-bought-from-several-suppliers

Take each supplier's embedded emissions per tonne and weight it by the tonnes you consumed from them in the period. Where a supplier gives no figure, use the default value for that share. Keep the purchase register that shows tonnes by supplier, because the verifier will check the weights.

## Steps

1. List tonnes consumed from each supplier in the reporting period.
2. Collect each supplier's figure and installation details.
3. Multiply and add, then divide by total tonnes used.

## Stock

Use tonnes consumed, not bought. Opening and closing stock shift the weights when purchases are lumpy.

## Worked example

- Mill A: 600 t at 2.0 t CO2 per t = 1,200 t CO2
- Mill B: 400 t at 2.5 t CO2 per t = 1,000 t CO2
- Weighted precursor figure: 2,200 / 1,000 t = 2.2 t CO2 per t

## What Senseible does here

Senseible reads fuel, power and production records into dated, fingerprinted installation records, the starting point for the actual emissions your EU importer asks for.

- [Where to find default values](https://senseible.earth/answers/where-to-find-official-cbam-default-values)
- [Fuel stock: bought or burned](https://senseible.earth/answers/fuel-stock-count-when-bought-or-burned)

Sources: [Implementing Regulation (EU) 2023/1773, monitoring rules](https://eur-lex.europa.eu/eli/reg_impl/2023/1773/oj/eng), [Implementing Regulation (EU) 2025/2621, CBAM default values](https://eur-lex.europa.eu/eli/reg_impl/2025/2621/oj/eng), [European Commission, CBAM legislation and guidance](https://taxation-customs.ec.europa.eu/carbon-border-adjustment-mechanism/cbam-legislation-and-guidance_en)

Last reviewed 2026-10-22.