Pilio uses DEFRA's Greenbuilding Gas Conversion Factors to estimate a building’s Carbon Footprint.

DEFA (Department for Environment, Food and Rural Affairs) is a UK Government body whose report offers the most up to date and accurate information on energy-to-carbon conversion factors. This information is freely available here. These factors are suitable for use by UK-based organisations of all sizes and international organisations reporting on UK operations.

The figure for electricity changes year on year because the means of producing electricity has changed – there are more renewable sources of energy like wind farms and solar panels supplying electricity to the National Grid.
These annual changes can be large as the factor depends also very heavily on the relative prices of coal and natural gas as well as fluctuations in peak demand and renewables.