How we calculate CO₂ per passenger

Every route page on this site shows an estimated carbon footprint per economy passenger. Here's exactly how we calculate it, what sources we use, and where the uncertainty lies.

The formula

CO₂_per_passenger = (great_circle_distance × emissions_factor) / load_factor

  • great_circle_distance: shortest distance between airport coordinates, in km.
  • emissions_factor: kg CO₂ per km flown, dependent on aircraft type. We use ICAO published values for the typical aircraft on the route (currently ~0.115 kg CO₂/km for narrow-body, ~0.135 for wide-body).
  • load_factor: average percentage of seats occupied (currently 0.82, IATA 2024 global average). Lower load = higher per-passenger share.

Sources we cite

  • ICAO Carbon Emissions Calculator (2024 update) — primary source for emissions factors per aircraft type.
  • IATA RP 1726 — Recommended Practice on per-passenger CO₂ calculation methodology.
  • atmosfair flight emissions database — secondary cross-check for long-haul figures.
  • OurAirports OSS dataset — for airport coordinates used in great-circle distance.

What our number includes

  • Direct CO₂ from jet-fuel combustion (passenger's share).
  • Adjustment for aircraft type typical on the route.
  • Average occupancy on commercial flights.

What our number does NOT include

  • Non-CO₂ effects (NOx, contrails, water vapor) — these can multiply climate impact 2–3× at altitude. We disclose CO₂ only because it's the standardized number; our footprint figure may understate true climate impact by a factor of 2.
  • Cabin class — Business and First class take more space per passenger (multiplier 2–4× Economy). Our figure is Economy-class equivalent.
  • Ground operations — taxiing, airport infrastructure, employee commute.
  • Manufacturing emissions of the aircraft (amortized).

Why we publish this

Travelers increasingly want to know the climate cost of their decisions. We're not here to lecture or shame — flying is a useful, sometimes necessary part of life. But informed choice requires honest data, even when imperfect.

For routes where rail is competitive (under 1500 km in Europe), we'll show the train alternative alongside, so you can compare. We don't discount flights we don't approve of.

How to reduce your aviation footprint

  1. Fly less. The single biggest factor.
  2. Fly direct. Connecting flights add 15–25 % due to extra take-off.
  3. Fly economy. First class footprint can be 4× economy on the same flight.
  4. Choose modern aircraft. A350 / 787 burn 20–25 % less fuel than 747 / A340.
  5. Take the train for short routes — 8 kg vs 95 kg CO₂ on Frankfurt→Munich.
  6. If you must fly, offset via a credible provider (Atmosfair, Wren) — not all offsets are equal; choose Gold Standard or Verified Carbon Standard.

Corrections welcome

If you spot a methodology error or have access to better data, email hello@online-check-in.com. We'll publish corrections with full attribution.