Aircraft CO2 emissions are an exact multiple of fuel consumption.
To calculate fuel consumption there are two different approaches for aviation (Method A and Method B).
CO2 emissions are then calculated by multiplying the mass of fuel by the emission factor:
EMISSIONS = Fuel Consumption (in tonnes) × Emission Factor (in CO2 kilograms per tonne of fuel)
Type of Fuel & Emission Factor (tCO2/tFuel)
Aviation Gasoline (AvGas) - 3.10
Jet gasoline (Jet B) - 3.10
Jet kerosene (Jet A1 or Jet A) - 3.15