The ability to estimate the space volume that a tree occupies, in various heights, is a crucial factor in designing the street trees schedule in pavements of new urban infrastructures. The dimensions of Acer negundo tree crown in various heights can be the basis for a better space management in the pavements of cities. In this study, the height and the crown width of the A. negundo street trees in the Greek cities of Orestiada and Alexandroupoli and the allometric relations that can be found between them, were investigated. Data from 117 street trees growing in semi-permeable pavements of the two cities were used. In each selected tree, the total height (H), and the maximum and minimum crown diameter (CW) were measured. The selected model (CW-H) for Alexandroupoli exhibits a coefficient of determination (R2) of 0.81. The R2 of the model selected for Orestiada is lower (R2 = 0.66). The R2 of the model selected using the complete dataset is 0.77. A. negundo appears to have greater crown width in Alexandroupoli compared to that of Orestiada. In Orestiada the conditions of growth were variable since in many cases the measured trees were under side shade, while this not the case in the corresponding trees in Alexandroupoli. The better fit of the selected model in Alexandroupoli compared to that of Orestiada is probably due to the more variable growth conditions of Orestiada.