Dimensioning approaches for regenerative supply concepts for existing buildings using the example of geothermal energy and photovoltaics. For the successful integration of renewable energy sources into the supply concept of existing and new buildings, the required areas on the plot and on the building should be considered at an early stage, because at this point there is still a considerable amount of decision-making freedom. So far, there are no suitable approaches for the dimensioning of these areas. In this paper, an approach is pursued using dimensioning diagrams, which represent essential ratio parameters. These diagrams were created as an example for a district in Freiberg with typical characteristic values for a multi-family house, the site-soil properties, radiation loads, etc. The parameters used for the design of geothermal collectors include the geometry (ratio of circumference to collector area) and the useful area-related heating energy demand. The optimum is determined by means of an economic efficiency analysis. The application potential of this diagram approach for the first estimation and area dimensioning is large and it can contribute by its low application effort substantially to reducing the hurdles for the use of regenerative energies and to strengthening their economically meaningful application.