GHG emissions calculation is the process of converting a company’s activity data, such as fuel, electricity and purchased goods, into tonnes of CO₂ equivalent using emission factors and global warming potentials, within defined organizational and operational boundaries.
What it covers
Calculation answers three questions in order: whose emissions count (organizational boundary), which emissions count (operational boundary and scopes), and how much each source emits (activity data, emission factors, GWPs). The results are compiled into a GHG inventory.
Organizational boundary
The GHG Protocol offers two approaches for deciding which entities and operations are included.
| Approach | Rule | When it fits |
|---|---|---|
| Equity share | Include emissions in proportion to your ownership | Joint ventures and partial holdings are significant |
| Control (operational or financial) | Include 100% of emissions from operations you control, none from those you don’t | Most companies; aligns with consolidated accounts |
Apply one approach consistently across the group. For disclosure under IFRS S2 or ESRS, start from the consolidation scope of your financial statements and explain any differences.
Operational boundary and scopes
- Scope 1: direct emissions from owned or controlled sources: stationary combustion, mobile combustion, process emissions and fugitive emissions such as refrigerant leaks.
- Scope 2: indirect emissions from purchased electricity, heat, steam and cooling, reported both location-based and market-based.
- Scope 3: all other indirect emissions in the value chain, in 15 categories. See Scope 3.
The formula and its inputs
Emissions (tCO₂e) = activity data × emission factor × GWP
- Activity data: measured quantities such as fuel volume, kWh, tonne-kilometers, or spend.
- Emission factor: emissions per unit of activity. Sources include national inventories, the IEA for grid electricity and commercial databases for Scope 3.
- GWP: converts methane, nitrous oxide and other gases into CO₂ equivalents. Use values from the latest IPCC assessment unless a rule specifies otherwise, and disclose the source.
Factor accuracy is described in tiers: Tier 1 uses default international factors, Tier 2 uses country- or fuel-specific factors and Tier 3 uses facility-specific measurements. Material sources should move to higher tiers over time.
Common pitfalls
- Mixing units (kWh vs. MWh, liters vs. cubic meters) or heating values (net vs. gross).
- Applying one year’s factor set to another year’s data.
- Double counting energy that is both generated and sold on site.
- Leaving out small sources: refrigerants, backup generators, leased vehicles.
- Using a market-based Scope 2 factor without valid contractual evidence.
How companies respond
- Document boundary decisions and the reasons for any exclusions.
- Keep an emission factor register with source, version and year for every factor used.
- Calculate monthly where possible so errors surface early.
Aentscope applies emission factors by country, industry and year automatically, keeps factor versions and sources on record and flags values that look off against previous periods.
Related regulations and standards
| Type | Name | Relevance |
|---|---|---|
| International standard | GHG Protocol Corporate Standard | Boundaries, scopes, calculation |
| International standard | GHG Protocol Scope 2 Guidance | Location- and market-based methods |
| International standard | GHG Protocol Scope 3 Standard | Value-chain calculation |
| International standard | ISO 14064-1 | Requirements for organizational inventories |