Buildings represent about 40% of the total primary energy consumption and contribute approximately to one-third of the total greenhouse gas emissions. Green building standards and certification systems include requirements for both new and existing buildings. However, a vast part of the existing building stock in cities was built with limited consideration for green design, energy efficiency and low carbon emissions, yet its refurbishment can help reach national energy reduction goals, decreasing environmental impact. Furthermore, retrofitting existing buildings can often be more cost-effective than building new facilities. The potential of an existing building to achieve certification under a certain Green Standard, defined in this work as its Green Potential (GP), depends heavily on factors that were determined during the original design and construction process. This paper will present the development of a method and tool for the analysis and determination of the GP of existing buildings, allowing quick evaluation of a single building or the comparison of different buildings in order to understand their potential and limitations, both by designers before their intervention or by planning authorities as ways of determining development plans and retrofitting potential in cities and districts.