What this calculator works out
This calculator multiplies flight distance by an emission factor per passenger-kilometre and by the number of passengers, giving the carbon dioxide attributable to the party.
The emission factor is the whole calculation, and published factors vary considerably — by aircraft, by cabin class, by haul length, and by whether non-CO₂ effects are included.
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Before you use a factor
- Short-haul flights have a higher factor per kilometre than long-haul, because take-off and climb consume a disproportionate share of the fuel.
- Cabin class matters substantially. Business and first class occupy more of the aircraft per passenger, and published factors reflect that with multipliers of two or more.
- The government publishes greenhouse gas conversion factors annually. Using the current set keeps the figure defensible.
- Distance should be the great-circle distance flown, not the map distance between cities.
Aviation also produces contrails, water vapour and nitrogen oxides at altitude, which together are estimated to roughly double or more the warming effect of the CO₂ alone. Published reporting factors often include an optional radiative forcing multiplier for this, commonly around 1.9. A figure quoting CO₂ only is not wrong, but it is not the whole impact either.
How this calculator works
Distance times factor times passengers:
Kilograms of CO₂ = distance in km × emission factor per passenger-km × passengersThe factor is per passenger, so multiplying by the number of passengers gives the total attributable to the party rather than to the aircraft. The aircraft's total emissions are divided among everyone on board, which is why a full flight has a lower per-passenger figure than an empty one.
The calculator holds no factor of its own, deliberately. Factors change annually and vary by haul and class, and a hard-coded value would go stale without any indication.
Worked example: a 1,500 km flight
Using the default figures — 1,500 km, 2 passengers, a factor of 0.15 kg per passenger-km:
- Total: 450 kg CO₂
450 kg for two people on a short-haul flight, one way. A return trip doubles it to 900 kg, and applying a radiative forcing multiplier of around 1.9 takes the warming-equivalent figure past 1,700 kg. For comparison, a typical UK household's annual home energy emissions are in the region of 2,000 to 3,000 kg — so one European return flight for two is a substantial fraction of a year's heating and electricity.
Common mistakes
- Using a long-haul factor for a short flight. Short-haul is higher per kilometre.
- Ignoring cabin class. Premium cabins carry multipliers of two or more.
- Calculating one way for a return trip.
- Omitting non-CO₂ effects without saying so. They roughly double the warming impact.
- Using a factor from an old publication. They are revised annually.
Frequently asked questions
Where do I get an emission factor?
The UK government publishes greenhouse gas reporting conversion factors annually, broken down by haul length and cabin class, with and without a radiative forcing uplift. They are the standard reference for UK reporting. Airline and comparison-site calculators use their own methodologies and can differ substantially from each other.
Does carbon offsetting work?
It is contested. Offsetting funds projects claimed to avoid or remove emissions elsewhere, and investigations have found that some schemes substantially overstated their benefit, particularly certain forestry credits. Removal-based offsets with robust verification are better regarded than avoidance-based ones. Offsetting is generally accepted as a supplement to reducing flying rather than a substitute for it.
Is flying less the only option?
For long distances there is currently no low-carbon alternative at scale — sustainable aviation fuels are a small fraction of supply and electric aircraft remain short-range. Within Europe, rail typically produces a small fraction of the emissions of the equivalent flight, and for journeys under about 1,000 km it is often competitive on door-to-door time once airport processes are counted.
How does flying compare with driving?
Per passenger-kilometre, a short-haul flight and a single-occupancy petrol car are broadly comparable, and a full car is considerably better than flying. The larger factor is distance: flights are taken over distances nobody would drive, so a single flight frequently exceeds a year of local car use regardless of the per-kilometre comparison.
Is what I enter stored?
No. Figures are processed in your browser and never transmitted or retained.
Related tools
References
- GOV.UK — greenhouse gas reporting conversion factors, including aviation by haul and class
- Met Office — climate science, including aviation's non-CO₂ effects
Sources are checked at publication and can change — how I choose and check references.