Small and medium-sized ports are important hubs in logistics chains and support 90% of the world’s seaborne trade. It is therefore crucial to achieve the decarbonization targets set by the European Union through the European Green Deal, as well as other EU transport policy objectives. The main objective of this work is to develop a web calculator of greenhouse gas (GHG) emissions related with the different transport modes to/from/in the ports of Aveiro and Figueira da Foz, located in the Centre region of Portugal. The calculator will follow the EMEP/EEA emissions calculation methodology, which is based on the energy consumption of transport and relates it to vehicle and fuel emission factors, thus providing reliable values for the GHG emissions released by vehicles during port operations. The calculator will be integrated into the website of the Port Administrations of these ports to be easily accessible to different types of users and to raise awareness of the consequences of the logistics and operational processes that take place in these ports.