The non-destructive study of historical buildings, archaeological sites and other Cultural Heritage structures requires high resolution methodologies and a good knowledge of the potential of the different methods. Laboratory measurements provide valuable information about the ability to detect different targets and to determine structural problems, but these data must be compared to the results obtained in real and complex structures. In this work, we present experimental GPR measurements made in order to determine the spatial resolution under laboratory conditions. These results were compared to the data obtained in different GPR surveys applied to Cultural Heritage. The information obtained in drillings, in visual inspections and in old documentation about the historical buildings and archaeological sites is used to determine the resolution in each case.