<p>This paper presents theoretical formulas for calculating the stress wave velocity in standing trees and logs based on the stress wave propagation equations for both. On this basis, a theoretical model for the conversion ratio of wave velocity between standing trees and logs is constructed. The accuracy and reliability of this theoretical model are verified through actual measurements of the wave velocity conversion ratio in several different tree species, and the following conclusions were obtained: the theoretical wave velocity conversion ratios for the tested tree species are all greater than 1.1. Radiata pine and loblolly pine have the highest theoretical conversion ratios, both at 1.19, while western hemlock has the lowest value at 1.10. The theoretical conversion ratio for larch used in this study is similar to that of radiata pine and loblolly pine, at 1.18. Except for loblolly pine, the theoretical conversion ratios for the other species are all lower than those of larch and radiata pine. This may be due to differences in species or factors such as moisture content. Therefore, when calculating the theoretical wave velocity conversion ratio for a specific species in the future, it is best to use the elastic constant values for that particular species in its green condition. The measured wave velocity conversion ratio for ponderosa pine is the highest at 1.36, while red pine has the lowest at 1.10. The difference between the measured and theoretical wave velocity conversion ratios for radiata pine is the smallest, at only − 0.8%, while the largest difference is for ponderosa pine, at 22.5%. Overall, except for western hemlock and ponderosa pine, the measured and theoretical conversion ratios for other species are relatively close, with differences within 10%. With the exception of a few species, the theoretical model for the wave velocity conversion ratio between standing trees and logs proposed in this paper is accurate and feasible.</p>