What Does the Emissions Figure on a Flight Booking Mean?

Search for a flight on Google Flights, Skyscanner or your company's booking tool and you'll often see an emissions figure next to each option, such as "142 kg CO2e", sometimes with a label like "Lower emissions" or "−12% emissions". This guide explains what that number means, where it comes from, why it changes from site to site, and whether you should use it for corporate reporting.

What emissions mean on a flight booking

The figure is an estimate of the greenhouse gas emissions attributable to one passenger on that specific flight, one way. It is usually shown in kilograms of CO2e (carbon dioxide equivalent), a unit that combines CO2 with other greenhouse gases, such as methane and nitrous oxide, weighted by their warming effect.

It is an estimate, not a measurement. The airline's actual fuel burn for your flight isn't known when you book, so booking sites model it from:

• Aircraft type and age: newer, more fuel-efficient aircraft burn less fuel per seat.
• Seating layout and cabin class: premium seats take up more space, so they are allocated a larger share of the flight's emissions.
• Load factor: the share of seats typically filled. A fuller flight spreads emissions across more passengers.
• Cargo: part of the fuel burn is allocated to freight carried in the hold.
• Distance and routing: including take-off and landing, which use a disproportionate amount of fuel on short flights.

Where the number comes from

Most of the figures you see come from a small number of sources:

• Google's Travel Impact Model (TIM): the model behind Google Flights, administered by Google and overseen by an expert advisory committee. It estimates "well-to-wake" emissions, covering fuel production and transport as well as the fuel burned in flight. It is also available to other travel companies, so many booking sites show the same numbers.
• The EU Flight Emissions Label: a voluntary scheme run by the European Union Aviation Safety Agency (EASA), launched in December 2024. Participating airlines' emissions are calculated using a harmonised EU methodology and their own verified data. Since July 2025, Google Flights uses these figures where they are available.
• Airlines and travel management tools: some airlines publish their own estimates, and corporate booking tools and TMCs may use TIM or a specialist emissions provider.

What "lower", "typical" and "higher" emissions mean

On Google Flights, each flight's estimate is compared with the typical emissions for the route you searched, which is the median across flights on that route. A flight is then labelled lower, typical or higher than that benchmark, and the percentage shows how far it sits from it.

These labels are relative to the route, not absolute. A "lower emissions" long-haul flight will still produce far more emissions than a typical short-haul one. A non-stop flight isn't always the lowest option either: aircraft type and seating layout can outweigh the extra take-off and landing on a connecting route.

Why the same flight shows different numbers on different sites

If you compare the same flight across sites, or against your company's emissions report, the figures often won't match. That is usually down to methodology rather than error:

The most common reasons for differences are whether well-to-tank emissions are included, whether a radiative forcing uplift is applied for aviation's non-CO2 effects, the load factor assumed, how emissions are split between cabin classes, and whether the distance is the direct route or the actual flight path.

What about contrails?

Contrails, the vapour trails aircraft leave at altitude, add to aviation's warming effect, but they are not included in the CO2e figure on Google Flights. Instead, Google shows a separate contrail impact rating of low, medium or high for each flight, reflecting how much extra warming its contrails are likely to cause relative to its CO2 emissions. The rating is based on historical weather patterns, so the actual effect on the day can differ.

Should you use booking-site figures for corporate reporting?

Booking-site figures are designed to help travellers compare options at the moment they book. Corporate reporting has a different job: it needs one consistent, documented methodology applied to every trip, so that your Scope 3 Category 6 figures can be compared year on year and stand up to assurance.

Mixing figures from different booking sites in one inventory produces numbers that aren't comparable. Choose a methodology, document it, and apply it to all your flight data. See what counts in Scope 3 Category 6, our guide to calculating air travel emissions, and the methodologies Thrust Carbon supports, including Google's Travel Impact Model, for consistent reporting across your programme.

Do emissions labels change what people book?

UK Department for Transport research found that carbon labels increased sustainable flight choices by up to 75%, although the study measured what people said they would book rather than what they actually booked, and price and convenience remained the main drivers. Read our summary of how emissions labels impact traveller booking behaviour.