Tree trunk diameter and tree species are two of the most important parameters in analyzing trees in urban areas and forests. Conventionally, diameters have been measured manually, and the species were determined by sight. An automated tool for these assessments was developed. Tree trunks are automatically detected from captured stereo images. Then, tree trunk diameters are estimated, and the species are determined. The developed graphical user interface tool enables fast and accurate estimation even while one is walking, which reduces the time spent in measuring trees.