A methodology, named ECAIS, is presented to calculate ship emissions based on their fuel consumption from AIS data. This is done to avoid use of commercial ship databases, which can be expensive for research on sizable fleets. Using the approximation method Holtrop-Mennen it is possible to find a distinct ships propulsion power requirements for different speeds. This empirical method uses main ship characteristics for calculation. From AIS data several main ship characteristics can be derived. Remaining characteristics is found by generic ship approximation found in literature surveys. This is used in combination with power prediction and specific fuel consumption, and applied to different ship size categories, as fuel consumption is calculated from speeds in dynamic AIS data. Fuel consumption and CO2 emission are derived and compared to earlier studies.