Street reverberation can strongly increase sound pressure levels in urban streets. In noise mapping models on the other hand, including a sufficient number of reflections is computationally very costly. A simple regression model is developed in this study, based on typical street width and façade height or façade roughness in old city centers of many European cities. This model is based on measurements with a mobile setup in 99 streets in the city of Ghent, Belgium, representative for common European city morphology. The reflection ratio (RR) is used as a parameter to determine the energy contained in the reverberation part of the sound field. The model has been successfully validated by detailed measurements at different source-receiver distances in an urban street canyon.