How we calculate flight CO₂
Step-by-step explanation of the ICAO Carbon Emissions Calculator v13.1 — the international standard used by airlines, the EU ETS, and corporate travel tools worldwide.
Emission factor
3.16
kg CO₂ / kg fuel
ICAO standard conversion from jet fuel (kerosene) weight to CO₂ mass via complete combustion chemistry.
RFI factor
1.9×
total climate impact
Non-CO₂ climate effects at altitude — contrails, NOₓ-driven ozone, methane destruction — multiplied over CO₂-only figure.
Standard
ICAO CEC
version 13.1 · 2023
The same methodology used for CORSIA airline reporting, EU ETS aviation, and GHG Protocol Scope 3 corporate travel.
Step by step
The six calculation steps
From airport coordinates to per-passenger CO₂ — how the ICAO v13.1 methodology works under the hood.
1. Great-circle distance
The calculator determines the shortest path between origin and destination airports using their geographic coordinates. This great-circle distance (in km) is the primary input for fuel burn estimation.
2. Fuel burn estimation
Fuel consumption per seat-km is derived from ICAO aircraft performance databases. When the specific aircraft type is known, actual type-specific fuel burn data is used. Otherwise, a distance-band fleet average applies (short-haul < 1,500 km, medium-haul 1,500–4,000 km, long-haul > 4,000 km).
3. CO₂ conversion
Total fuel burn (kg) is multiplied by the ICAO emission factor of 3.16 to convert jet fuel weight to CO₂ mass. This factor accounts for the complete combustion of kerosene (C₁₂H₂₆) to CO₂ and H₂O.
4. Seat-class allocation
Total flight CO₂ is distributed across passengers weighted by seat floor area (Y-seat factor). Economy class has a factor of 1.0; business class typically 3.0–4.0; first class 4.0–6.0. This reflects the space each passenger occupies on the aircraft.
5. Load factor adjustment
The passenger load factor (PLF) — the proportion of seats occupied on average — adjusts each passenger's share. At a PLF of 82%, empty seats' emissions are distributed across paying passengers. ICAO uses route-specific load factors from IATA traffic statistics.
6. RFI (optional)
Multiplying by the Radiative Forcing Index (1.9) accounts for non-CO₂ climate effects at cruising altitude: contrail formation, ozone production from NOₓ, methane destruction, and water vapour. The GHG Protocol recommends CO₂-only for corporate Scope 3 reporting.
Formula
The calculation formula
// Step 1–2: total aircraft fuel burn
fuel_kg = distance_km × fuel_per_seat_km × total_seats
// Step 3: convert to CO₂
total_co2_kg = fuel_kg × 3.16
// Step 4–5: allocate to passenger
passenger_co2_kg = total_co2_kg × yseat_factor / (total_seats × load_factor)
// Step 6: optional RFI adjustment
passenger_co2_rfi_kg = passenger_co2_kg × 1.9
Y-seat factors (typical)
Fleet-average fuel burn
Compliance coverage
Which reporting frameworks does ICAO CEC v13.1 satisfy?
ICAO CEC v13.1 is the calculation engine recognised across all major corporate sustainability reporting frameworks.
GHG Protocol
RecognisedScope 3 Category 6 — Business Travel
ICAO CEC v13.1 is the recommended aviation methodology in the GHG Protocol Scope 3 Calculation Guidance. Returns co2_kg for direct use in Category 6 reporting.
CSRD / ESRS E1
RecognisedE1-6 — GHG Emissions disclosure
ESRS E1-6 requires Scope 3 Category 6 data for large EU companies from fiscal year 2024. ICAO CEC v13.1 satisfies the methodology transparency requirement for external auditors.
CDP Climate
RecognisedC6.5 — Scope 3 Category 6
CDP requires Scope 3 Category 6 in tCO₂e. Divide co2_kg by 1,000 to get tCO₂e for the CDP submission template.
ISO 14083:2023
RecognisedTransport chain GHG emissions
ISO 14083 defines the allocation framework for transport chain emissions. ICAO CEC provides the aviation segment fuel burn data required by the standard.
Data sources and references
ICAO Carbon Emissions Calculator v13.1 (2023)
Primary methodology. Includes aircraft fuel consumption data, load factor statistics, and seat-class allocation.
ICAO CORSIA Eligible Fuels Life Cycle Assessment (2022)
Upstream emission factors for jet fuel production, used for supply-chain-complete LCA calculations.
IATA World Air Transport Statistics (WATS)
Passenger load factors by route and airline, updated annually. Used as default PLF in fleet-average calculations.
EU ETS Aviation (Directive 2003/87/EC)
Regulatory framework for aviation CO₂ emissions in the EU. Offset prices sourced from ICE exchange ETS carbon futures.
GHG Protocol Scope 3 Standard – Category 6: Business Travel
Corporate accounting framework. Recommends CO₂-only (without RFI) for Scope 3 business travel reporting.
ISO 14083:2023 – Quantification and reporting of GHG emissions from transport chain operations
International standard for transport chain GHG accounting. ICAO CEC v13.1 provides the aviation segment data required by ISO 14083.
CSRD / ESRS E1 – Climate change (European Commission, 2023)
EU Corporate Sustainability Reporting Directive. ESRS E1-6 requires Scope 3 Category 6 (business travel) disclosure. Applies to large EU companies from fiscal year 2024.
FAQ
Methodology FAQ
Try the calculator
Calculate exact CO₂ for any route using this methodology.