How we calculate flight emissions

Our flight emissions calculator estimates the total climate impact of your flights, not just the CO₂ from burning fuel, but the full warming effect of flying at high altitude. Here's how it works, and why it matters.

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What we measure

When you fly, the climate impact goes beyond the CO₂ released by burning jet fuel. Our calculator accounts for the full climate impact of your flight:

• Direct CO₂ emissions from burning fuel during the flight

• Upstream CO₂ emissions from extracting, refining, and transporting the fuel before it reaches the aircraft

• Non-CO₂ warming effects such as contrails, nitrogen oxides, and water vapour released at high altitude

How accurate is it?

The calculator uses one of two levels of precision depending on what information you provide:

For the best results, enter your flight number and departure date whenever possible.

Where your emissions data comes from

Our primary data source is the Google Travel Impact Model (TIM). This model factors in aircraft type, fuel efficiency, how full the plane is, seat configuration, cabin class, and route distance. It's widely used across the travel industry, including in Google Flights.

How the calculation works

1. Base CO₂ emissions

We retrieve per-passenger CO₂ emissions for your flight from the Google Travel Impact Model. This covers both the fuel burned during the flight and the emissions from producing and transporting that fuel.

2. Passengers and return flights

We multiply the per-passenger emissions by the number of passengers in your booking. For return flights, the emissions are doubled.

The doubling of emissions for return flights is a known simplification. In reality, wind patterns can make one direction slightly more or less fuel-intensive than the other. We are looking into improving this.

3. Non-CO₂ climate effects

Flying at high altitude produces warming effects beyond CO₂, including contrails and cirrus clouds that trap heat, nitrogen oxides that affect ozone and methane levels, and water vapour released where it has a stronger warming effect.

These non-CO₂ effects are estimated at 70% of the direct combustion CO₂. This is a moderate, science-based estimate. It is not the highest figure in the literature, and not the lowest.

4. Total climate impact

Your total emissions in CO₂-equivalent (CO₂e) are the sum of direct CO₂, upstream CO₂, and non-CO₂ effects. All results are shown in kilograms of CO₂e, rounded to the nearest whole kilogram.

Putting it in context

To help you understand what the numbers mean, we convert your flight emissions into everyday equivalences:

What you should know

• Non-CO₂ effects are estimated. The actual impact of contrails and other effects varies with altitude, weather, time of day, and season. Our multiplier represents a moderate central estimate from published research, not a precise measurement.

• Aircraft load factors are built in. The Google Travel Impact Model already accounts for how full the plane typically is.

• Return flights assume equal legs. In reality, wind patterns can make one direction slightly more fuel-intensive than the other.

• Distances shown are indicative. We display an approximate range using a great-circle formula. The actual emissions calculation accounts for routing separately.

Sources and references

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