Calculating your Scope 3 emissions from your accounting:
the monetary method explained.

The principle: from euros to tonnes of CO₂

The monetary method rests on a simple idea: every euro spent in an economic sector generates an average amount of CO₂. ADEME maintains a database, the Base Empreinte (formerly Base Carbone), which contains these ratios for every French business sector, identified by its NAF code.

The basic formula is: Emissions (kgCO₂e) = Amount excl. tax (€) × ADEME monetary ratio (kgCO₂e/€)

For example, if you spent €200,000 excl. tax on steel purchases and the ADEME monetary ratio for the steel sector is 1.2 kgCO₂e per euro, your emissions related to these purchases are 240 tonnes of CO₂ equivalent.

It’s less precise than a calculation based on physical data (tonnes of steel × physical factor), but it’s immediately applicable from your accounting export, without any additional data collection.

Step 1: extract class 6 expenses

Your accounting is organized according to the French Chart of Accounts (Plan Comptable Général, PCG). Operating expenses are in class 6. That’s where your Scope 3 data is found.

Export your general ledger or trial balance from your accounting software (FEC, Pennylane, Sage, or any tool capable of producing a CSV/Excel file). You need four columns: entry date, account number, description, and amount excl. tax.

The accounts that matter for Scope 3:

• 601-602-607: Raw materials, supplies, goods for resale → GHG Category 1 (Purchased goods and services)
• 604, 611-617, 622-623, 626: External services → GHG Category 1 (Purchased services)
• 605, 681: Capital assets, depreciation → GHG Category 2 (Capital goods)
• 6061: Water, energy → GHG Category 3 (Upstream energy)
• 624: Transport of goods → GHG Category 4 (Upstream transportation)
• 625: Travel, business trips → GHG Category 6 (Business travel)
• 612-613: Leasing, rentals → GHG Category 8 (Leased assets)

Excluded accounts: taxes and duties (631-637), wages (641-648), financial expenses (661-668) and exceptional expenses (671-678) do not generate direct emissions and are excluded from the Scope 3 calculation. This exclusion complies with the GHG Protocol and is documented in the report.

Step 2: apply the ADEME monetary ratios

Once your expenses are extracted and categorized, you apply the monetary ratio corresponding to each type of expense. These ratios are available in the ADEME Base Empreinte, broken down by NAF sector.

Concrete example for a mechanical engineering SME (NAF 2562B):

Material purchases (accounts 601-602): €450,000 × 0.85 kgCO₂e/€ = 382.5 tCO₂e
External services (604, 611-617): €120,000 × 0.42 kgCO₂e/€ = 50.4 tCO₂e
Freight transport (624): €35,000 × 1.10 kgCO₂e/€ = 38.5 tCO₂e
Business travel (625): €28,000 × 0.65 kgCO₂e/€ = 18.2 tCO₂e
Energy (6061): €42,000 × 0.55 kgCO₂e/€ = 23.1 tCO₂e
Rentals (612-613): €18,000 × 0.30 kgCO₂e/€ = 5.4 tCO₂e

Estimated total Scope 3: 518.1 tCO₂e

Monetary ratios vary by sector. Purchases in the steel industry have a high ratio (high carbon intensity), while IT services have a low ratio. That’s why it’s important to use the most precise sector-specific ratios possible, rather than an average ratio across all sectors.

Step 3: refine with physical data (optional)

The monetary method gives an immediately usable result. But if you have certain physical data available, you can improve the accuracy of the calculation.

Energy: if you know your consumption in kWh (EDF/Engie bills), use the ADEME physical factor for French electricity (about 0.052 kgCO₂e/kWh) rather than the monetary ratio. It’s much more precise.

Transport: if you know the distances traveled and the modes of transport (road, sea, air), the ADEME physical factors per tonne-kilometer are more reliable than the monetary ratio.

Business travel: if you can distinguish flights (account 625 with a description containing “plane” or “Air France”) from train or car journeys, the factors per passenger-kilometer give a much more precise result.

In an Oakbon report, each emission line is classified as “precise” (physical factor) or “estimated” (monetary ratio). The overall precision score indicates what proportion of emissions is based on physical data. The higher this score, the more credible the report is with your client.

Limitations to keep in mind

The monetary method has limitations that must be acknowledged and documented in the report.

Inflation distorts the calculation. If steel prices rise by 20% without any change in volumes, your calculated emissions increase by 20%, which is incorrect. ADEME factors are updated annually to limit this effect, but the lag still exists.

The average ratio masks differences. Two steel suppliers can have very different carbon intensities depending on their energy mix and location. The ADEME monetary ratio gives a sector average, not the specific footprint of your supplier.

Some categories fall outside accounting records. Waste (GHG Category 5) and employee commuting (Category 7) do not generate direct accounting entries. Oakbon estimates them via the guided questionnaire, using sector averages and INSEE data.

Despite these limitations, the monetary method is the method recommended by ADEME for SMEs getting started. It makes it possible to produce a first credible carbon footprint, aligned with the GHG Protocol and ESRS standards, from data you already have.

Key takeaway: Don’t let the pursuit of precision stop you from starting. A carbon footprint based on the monetary method, using official ADEME ratios, is infinitely more useful than a perfect footprint that never gets done. You can refine it with physical data in subsequent years.

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