Jarul (Lagerstroemia speciosa L. Pers., Family- Lythraceae) is a semi-deciduous medium to large-sized tree with fluted bole, small buttress and slightly flaky bark tropical flowering tree species. It is a common ornamental tree planted along roadsides, gardens and parks in Bangladesh. The main aim of this study is to develop mathematical models for total volume estimation of jarul. To meet the quest we have tested 21 models for volume equation by regression technique. The best-fitted model for studied species have been selected by highest value of R2 (coefficients of determination), the lowest value of Akaike Information Criterion (AIC) and Root Mean Square Error (RMSE). The selected models also validated by Chi-square test of goodness of fit, Paired t-test, Percent Absolute Deviation (%AD) and 45 degree line test. The study appearance that, for one way analyses the model ln (V) = a+b ln (D) and for two way analyses ln (V)= a+b ln (D)+c ln (H) appeared to the best model for estimating the standing tree volume of jarul. Conversion factors equation has been determined to estimate under bark volume and under bark volume of different top end girth of 30, 35, 40 and 45 centimeters from these models. The best-fit volume model showed the highest efficiency in volume estimation compared to previous developed volume model of this species in terms of Model Prediction Error (MPE), Model Efficiency (ME) and Root Mean Square Error (RMSE).