The formula, and why distance alone isn't the whole answer
Fuel burn per passenger-kilometre is fairly steady — about 0.03 kg of fuel — and each kilogram of jet fuel makes 3.16 kg of CO₂. But two multipliers change the answer a lot: the cabin class (economy is the baseline) and the RFI, which accounts for warming beyond CO₂. Real routes also run about 9% longer than the straight-line distance.
Short hops are the worst per kilometre
Take-off and climb burn a disproportionate amount of fuel, so a short flight emits more per kilometre than a long one. The distance still makes a long-haul trip larger overall, but per km the short hop loses.
Per kilometre, a short flight burns the most fuel — which is why a train often wins on the routes where it competes.
Cabin class multiplier
| Cabin | Multiplier | Meaning |
|---|---|---|
| Economy | ×1.0 | Baseline seat footprint |
| Premium economy | ×1.6 | Wider seat, more space |
| Business | ×2.0–3.0 | Lie-flat seats take 2–3 economy spaces |
| First | ×3.0–4.0 | A suite can equal 4–5 economy seats |
One first-class seat can carry as much CO₂ as three or four economy passengers on the exact same flight.
The two things people get wrong
- RFI is not optional padding. Contrails and NOx at altitude roughly double or triple the warming. A CO₂-only figure understates a flight\'s real climate impact by 2 to 3 times.
- The 3.16 factor is fixed. Burning jet fuel always makes 3.16 kg of CO₂ per kg of fuel — it\'s chemistry. What changes the total is how much fuel your seat is charged for, not this number.
Common questions
How much CO2 does a flight produce per passenger?
As a rough guide, count about 90 kg of CO2 per hour of economy flying, or 100 to 250 kg for a one-way medium-haul trip. A New York to London economy seat is roughly 1 tonne of CO2 round trip, or closer to 2.5 tonnes once the non-CO2 warming effects are included.
What is the radiative forcing index?
Planes warm the climate with more than just CO2 — water vapour, nitrogen oxides and contrails add to the effect at altitude. The radiative forcing index (RFI) multiplies the CO2 figure to account for this, usually by 2 to 3. So a flight that burns fuel for 100 kg of CO2 has a total warming impact nearer 200 to 300 kg.
Why does business class emit more than economy?
The plane burns the same fuel either way, but a business seat takes up 2 to 3 times the floor space of an economy seat. The fuel is shared out by space, so a business passenger is charged for 2 to 3 economy seats' worth. A first-class seat can be 3 to 4 times as much.
