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How does your calculator work?

Once you have entered data into the calculator, we multiply it by emissions factors. For example, if you input that you have driven a certain number of miles in a large petrol car, we multiply that distance by a factor showing the greenhouse gases released for each mile.

The emissions included are the three major greenhouse gases: carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). 

As well as the direct emissions associated with an activity, we also include the indirect emissions.  For example as well as the exhaust fumes from driving we also include the emissions associated with getting the petrol to the pump in the first place.

The emissions factors we use and the methodology behind the calculator follow the UK government's guidelines for calculating a carbon footprint.

In order to calculate the carbon emissions associated with a flight, we need to know the distance travelled. To calculate this, we ask you to provide the origin and destination airports. We then use the latitudinal and longitudinal coordinates of these places to work out the distance between them, and then increase this by 9% (recommended by Defra to account for non-direct flight paths and stacking at airports during periods of heavy congestion). Our international flight calculations assume travel in economy class.

For flights we also take account of radiative forcing. Radiative forcing is the name for the additional impact that flight emissions have on the environment because of other gases and emissions produced, as well as the fact that they are being deposited directly into the upper atmosphere. To account for this, the emissions are multiplied by a factor of 1.9, as recommended by the Department for Transport and the IPCC.

If you have used a calculator on another website, you can offset the footprint that it came up with by entering it into our website.

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