To calculate your footprint on animals, we use FarmKind’s calculator, here. FarmKind explains how it works here. We also use FarmKind’s calculator to determine how much it costs to offset your animal and carbon footprints.
For electric car efficiency, we use
| BEV electric efficiency | 3.60 | mi/kWh | https://afdc.energy.gov/vehicles/electric-emissions-sources |
|---|
To calculate electric car emissions, we use the efficiency above combined with the user’s country data, if available. Otherwise, we default to .24 lbs CO2/mi. For plugin hybrids we use .42 lbs CO2/mi. For gas cars 1.09 lbs CO2/mi, for hybrids .6 lbs CO2/mi.
| Type | Unit | kg CO2e | kg CO2e of CO2 per unit | kg CO2e of CH4 per unit | kg CO2e of N2O per unit |
|---|---|---|---|---|---|
| Average local bus | passenger.km | 0.10846 | 0.10772 | 0.00001 | 0.00073 |
| Type | Unit | kg CO2e | kg CO2e of CO2 per unit | kg CO2e of CH4 per unit | kg CO2e of N2O per unit |
| Light rail and tram | passenger.km | 0.02860 | 0.02832 | 0.00012 | 0.00016 |
| London Underground | passenger.km | 0.02780 | 0.02753 | 0.00011 | 0.00016 |
Source: UK Department for Energy Security and Net Zero 2024 conversion factors
For bus: we use “Average local bus” and 20km/hr speed.
For light rail or subway: we use the average of “Light rail and tram” and “London Underground" (.0282). We assume a speed of 40km/hr. If no mode of transportation is specified, we use the average of bus and metro.
For e-bikes, we use 4.9 g CO2e/mi (source) and assume a speed of 15km/hr. Note that this does not include lifecycle emissions, which is estimated to be around 20-25 g lifecycle CO2e per person kilometer (source).
We use the TIM model to estimate emissions per ticket, which is the model Google uses: https://travelimpactmodel.org/
Short flights: 123 kg CO2e, typical for flights from London to Rome
Medium flights: 389 kg CO2e, typical for flights from NYC to London
Long flights: 888 kg CO2e, typical for flights from LA to Sydney