How this instrument works
A flight's carbon footprint depends on more than the straight-line distance between two airports: cabin class matters (a first-class seat claims a larger share of the plane's total emissions than an economy seat), and so does haul length (short domestic hops burn proportionally more fuel per kilometre than long-haul cruising, because taxiing, takeoff and climb are fixed costs regardless of trip length). This calculator multiplies your entered distance by an emission factor chosen for haul class and cabin, giving a kg CO2e figure specific to that combination.
The factors are the UK Government's official 2026 GHG Conversion Factors for company and personal reporting, published by the Department for Energy Security and Net Zero (DESNZ) on 11 June 2026 — specifically the 'including indirect effects' passenger-km factor set, which is DEFRA's own recommended default when the goal is a full-impact estimate rather than a bare fuel-burn number.
Two adjustments are already built into every factor here, and this is worth disclosing plainly: each figure already includes an 8% distance uplift for non-direct routing (real flights rarely follow the great-circle path air-traffic control actually assigns, plus holding patterns and diversions), and a roughly 70% uplift for non-CO2 climate effects — contrails, nitrogen oxides and water vapour at altitude, expressed via a radiative forcing multiplier. Don't add either adjustment again on top of this calculator's output; it would double-count an effect the factor already accounts for.
- Enter the flight distance in kilometres — a one-way great-circle distance between airports is fine; the factor already adds a routing uplift.
- Choose a haul class and cabin — domestic, short-haul, long-haul (economy, business or first), or an international average.
- Read the CO2e emissions in kilograms — this is the DESNZ 'including indirect effects' full-impact estimate for that trip.
- Do not add any further margin for routing detours or non-CO2 effects — both are already priced into the emission factor.
Worked example — a 5,000 km long-haul-average flight
A 5,000 km trip flown at the long-haul-average factor of 0.15282 kg CO2e per passenger-km comes to 5,000 × 0.15282 = 764.1 kg CO2e. That figure already has the 8% routing uplift and the roughly 70% non-CO2 effects uplift baked in — it's a full-impact number ready to report or compare as-is.
Compare that to an 800 km domestic hop at the domestic factor of 0.22928 kg CO2e per passenger-km: 800 × 0.22928 = 183.424 kg CO2e. Per kilometre flown, the short domestic trip is markedly less efficient than the long-haul flight — taxi, takeoff and climb burn roughly the same fuel whether the flight covers 800 km or 5,000 km, so those fixed costs are spread over far fewer kilometres on the shorter trip.
Questions
Why does this calculator use distance and haul class instead of flight duration?
The DESNZ 2026 conversion factors this calculator is built on are published on a per-passenger-kilometre basis, broken out by haul class and cabin, which lets the same trip be estimated differently for economy versus business versus first class. A duration-based approach can't make that cabin-class distinction, since flight time doesn't change with seat class — distance and haul class is the more granular, defensible method for a full-impact estimate.
Should I add extra margin for indirect routing or radiative forcing effects?
No. Every factor in this calculator is DESNZ's 'including indirect effects' figure, which already bakes in an 8% distance uplift for non-direct air-traffic routing and a roughly 70% uplift for non-CO2 climate effects like contrails and nitrogen oxides at altitude. Adding either adjustment again on top of the calculator's output would double-count an effect the factor has already priced in.
Why is first class so much higher than economy for the same flight?
A plane's total emissions are allocated across passengers by the cabin space and weight each seat class occupies, not evenly per head. First-class seats are larger, spaced further apart, and carry a smaller headcount for the same length of cabin, so each first-class passenger is assigned a proportionally larger share of the aircraft's total fuel burn than an economy passenger on the identical flight.
Where do these emission factors come from?
The UK Government's Greenhouse Gas Conversion Factors for company reporting, published annually by the Department for Energy Security and Net Zero (DESNZ, formerly BEIS/DEFRA). This calculator uses the 2026 edition, published 11 June 2026, specifically the passenger-km, 'including indirect effects' factor set — DEFRA's own recommended default for a full-impact estimate rather than a bare direct-CO2 figure.
Does this calculator account for connecting flights or layovers?
No — enter each leg of a multi-flight itinerary separately and add the results, since emission factors and haul-class classification can differ leg by leg (a domestic connector followed by a long-haul segment, for example). Entering one combined origin-to-final-destination distance would misclassify the trip's haul class and understate the fixed per-flight costs of the extra takeoff and landing.