How to calculate Scope 3 emissions in Excel

Every Scope 3 calculation follows the same structure: an amount of activity multiplied by an emission factor for that activity.

• E — emissions, in kg CO₂e
• AD — activity data: the amount of activity, such as kg purchased, tonne-km shipped or kWh used
• EF — emission factor: the emissions per unit of activity, such as kg CO₂e per kg

Applied to each activity i and summed, it gives your total Scope 3 emissions:

When your emission factors are given per gas rather than in CO₂e, calculate each gas separately and convert with its global warming potential (Step 8):

이 GHG Protocol Corporate Value Chain (Scope 3) Standard divides value-chain emissions into 15 categories. Start by screening all 15 to find the ones that matter most for your company, then focus data collection there.

Report every relevant category, and document the reason for any category you exclude. The inventory should cover all seven Kyoto gases: CO₂, CH₄, N₂O, HFCs, PFCs, SF₆ and NF₃.

Four methods are used in practice. They share the same equation; what differs is the quality of the data behind each factor.

Spend-based factors come from environmentally extended input–output (EEIO) models and are expressed per unit of currency (kg CO₂e per USD, for example). Use them for screening and fill gaps with physical data as it becomes available.

Activity data is the backbone of the inventory. Record one row per activity, with the quantity, its unit and the emission factor it links to.

Typical sources are purchase orders and invoices, ERP exports, carrier reports, travel booking data, employee surveys, waste manifests and supplier questionnaires. Record the source and a data quality rating (primary, secondary or estimated) for every row.

Match each activity to an emission factor with the same unit, geography and system boundary. Follow this order for every row:

• Identify the activity data type and its unit
• Find a factor with a matching unit
• Convert the activity unit if it does not match (Step 6)
• Check the factor’s system boundary
• Apply the factor, convert gases to CO₂e, and aggregate

A key boundary rule: life cycle factors for fuels already include combustion. For Category 3, use only the upstream part, or you will double-count Scope 1:

Common factor sources include government sets (UK DESNZ conversion factors, US EPA Emission Factors Hub, Japan’s national factors), international bodies (IPCC, IEA, ICAO, IMO, the GLEC Framework for freight), life cycle databases (ecoinvent, 전문가를 위한 LCA (GaBi), IDEA for Japan) and EEIO models (USEEIO, EXIOBASE).

The activity unit must match the factor’s denominator. Convert before multiplying.

Freight is the most common conversion. A 25-tonne shipment over 800 km is:

Each category applies the core equation to its own activity data. Use this formula library:

When you have emissions per gas, multiply each by its 100-year global warming potential (GWP) and add them up:

Example: 10 kg of fossil methane is 10 × 29.8 = 298 kg CO₂e. Use one GWP set consistently across the whole inventory, and state which one you used.

A clean model separates inputs, factors and calculations, so every number can be traced. The free DEISO calculator uses this structure:

• Activity_Data — the only sheet you type in: one row per activity
• EF_Library — the controlled list of emission factors, with source and boundary
• GWP_Table — global warming potentials for gas-specific factors
• Unit_Conversion — conversions and small calculators for tonne-km and commuting
• Calc — formulas only: pulls each factor and calculates emissions
• QA_Checks — automatic checks for missing data and mismatches
• Summary — totals by category, shares and a chart
• Source_Log and Assumptions — the audit trail for every factor and assumption

The key formula looks up the factor for each row and multiplies it by the quantity. In Excel 365:

For compatibility with every Excel version, the calculator uses INDEX and MATCH:

When a factor is given per gas instead of in CO₂e, the calculator switches automatically to the gas route: CO₂ + CH₄ × GWP + N₂O × GWP.

Before you report, check the inventory for the errors that most often distort Scope 3 results:

In Excel, a missing-factor check is as simple as =COUNTIF(Activity_Data!K:K,"") for the rows you have filled. All checks should pass before the numbers leave the workbook.

Sum the row results by category, and report each category’s share of the total. The example data from Step 4 gives:

Common Scope 3 mistakes

• Double-counting fuel — using a full life cycle factor in Category 3 instead of the upstream part only
• Unit mismatches — multiplying tonnes by a factor per kg, or kilometres by a factor per tonne-km
• Mixed GWP sets — combining AR5 and AR6 values in one inventory
• Spend-based only — never moving the largest categories to physical or supplier data
• No audit trail — factors without a recorded source, year and boundary

Scope 3 calculation: frequently asked questions

Need a Scope 3 inventory built for you?

DEISO builds GHG Protocol and ISO 14064-1 inventories, including Scope 3 screening across all 15 categories and Scope 3-only inventories.