Carbon and GHG conversion factors from Defra (UK).

The purpose of the greenhouse gas (GHG) conversion factors is to help businesses convert existing data sources (e.g. utility bills, car mileage, refrigeration and fuel consumption) into CO2 equivalent emissions by applying relevant conversion factors (e.g. calorific values, emission factors, oxidation factors).

Carbon Calculated have standardised this information and made it available to developers via a RESTful API.