What is radiative forcing and why does it matter for flights?

Aircraft emit at altitude, where contrails and nitrogen oxides cause additional warming beyond the CO2 alone. Radiative forcing accounts for this. A common multiplier is around 1.9, so the climate impact of a flight is roughly double the CO2 figure on its own.

Why do business and first class emit more?

Premium cabins take up far more floor space per passenger, so each traveller is allocated a larger share of the aircraft's fuel burn. DEFRA applies multipliers of about 1.5 for premium economy, 2.9 for business, and 4.0 for first relative to economy on long-haul.

How accurate is a distance-based estimate?

Distance-based factors are the industry standard for travel reporting and are accurate to within a reasonable margin for accounting purposes. Actual emissions vary with aircraft type, load factor, routing, and weather, so treat the figure as a sound estimate rather than a measured value.

How is the offset cost calculated?

The tool multiplies your total CO2e in tonnes by a per-tonne carbon price you can adjust. Voluntary offset prices commonly range from around 10 to 40 units per tonne depending on project quality, so the default is a mid-range figure.

Should I count the return flight?

Enter one-way distance for a single leg, or double the distance for a round trip. The per-passenger figure scales linearly with distance, so a return trip is simply twice the one-way emissions for the same route and cabin.

Flight Carbon Footprint Calculator

Flying is one of the most carbon-intensive things most people do, and the true climate impact is larger than the CO2 alone because emissions at altitude cause extra warming. This calculator applies haul-specific emission factors, a cabin multiplier, and a radiative forcing uplift to give a realistic CO2e figure and the cost to offset it.

How it works

base kgCO2 per pax = distance_km × haul factor (kg/pax-km)
cabin adjusted      = base × cabin multiplier
with forcing        = cabin adjusted × radiative forcing (≈1.9)
total CO2e          = with forcing × passengers
offset cost         = (total CO2e / 1000) × carbon price per tonne

Haul factors fall with distance because take-off and climb burn disproportionate fuel on short hops: roughly 0.15 kg/pax-km for short-haul, 0.12 for medium, and 0.10 for long-haul flights in economy.

Cabin multipliers

Relative to economy on the same route: premium economy ≈ 1.5×, business ≈ 2.9×, and first ≈ 4.0×. These reflect the larger floor area each premium seat occupies, so the aircraft’s fuel is shared among fewer passengers.

Notes

Use one-way distance for a single leg and double it for a return trip. The radiative forcing multiplier is a modelling choice — some bodies report CO2 only and some apply 1.9 — so the tool shows both the CO2-only and forcing-adjusted figures.