This is a general estimate using a widely cited average emissions factor per passenger-kilometre. Actual emissions vary by aircraft type, load factor and routing, and different published methodologies (ICAO, DEFRA, individual airlines) can give noticeably different figures for the same flight.
Anyone who has compared two different flight emissions calculators has probably noticed they rarely agree, sometimes by a wide margin for the identical route. This happens because there is no single universally agreed methodology — different bodies like ICAO, DEFRA and individual airlines use different assumptions about aircraft fuel burn, seating density, cargo weight offsets and radiative forcing effects at altitude, all of which shift the final number. This calculator uses a widely cited general approach based on distance and cabin class, useful for comparing routes and options against each other, rather than claiming to match any one official reporting standard exactly.
Similar to how short flights carry disproportionately high monetary cost per kilometre because of fixed take-off and landing costs, they also carry disproportionately high emissions per kilometre for much the same reason: take-off and initial climb are the most fuel-intensive phases of any flight, and those fixed costs are spread over fewer kilometres on a short hop than a long one. This is why a single short-haul flight can sometimes have a comparable or even higher per-kilometre footprint than a long-haul flight, despite carrying far fewer total passengers to a further destination.
A business or first class seat takes up substantially more physical cabin space than an economy seat, which means fewer total seats are sold per flight and each remaining seat is responsible for a correspondingly larger share of the aircraft's total fuel burn. This is the reason premium cabin emissions factors used across most published methodologies run several times higher than economy for the identical flight — the aircraft, fuel burn and distance are unchanged, but the space and weight allocation per passenger is not.
This calculator is genuinely useful for comparing options before booking — direct versus connecting routings, economy versus a premium cabin, or one destination against another for a similar type of trip — since the same methodology applied consistently across options gives a fair relative comparison even if the absolute number carries some uncertainty. It is less suited to precise personal carbon accounting or offsetting calculations that require a specific, audited methodology, for which a dedicated carbon accounting service or your airline's own published figures (where available) would be more appropriate.
Where a direct flight and a connecting flight cover a similar total distance, the direct option is almost always the lower-emission choice, since extra take-offs and landings on a connecting itinerary add meaningfully to the total. For routes under a few hundred kilometres with a reasonable rail alternative, ground transport frequently produces a fraction of the emissions of the equivalent short flight. Beyond route and mode choices, many airlines and third-party providers offer verified carbon offset programmes for travellers who want to address the emissions of trips that can't practically be avoided.
Because there's no single agreed global methodology — different calculators use different assumptions about aircraft type, seating density, cargo offsets and altitude effects. Use one calculator consistently to compare your own options rather than treating any single number as an absolute truth.
Under most published methodologies, yes, because a business seat takes up several times the cabin space and weight allowance of an economy seat, meaning it's responsible for a proportionally larger share of the flight's total fuel burn.
Generally yes, since each additional take-off and landing adds a fuel-intensive phase that a direct route with only one take-off and landing avoids, even if the total distance flown is similar.
Treat this as a general planning estimate for comparing options rather than a precise offsetting figure. For an actual offset purchase, use the specific calculation method required by your chosen offset provider or your airline's own published passenger emissions figure where available.