Effective inventory methods are crucial for managing short-rotation plantations. This study evaluates the aboveground biomass and morphometric characteristics of four-year-old Eucalyptus hybrid DH3229. We used a stratified random sampling method to destructively sample 30 trees from a low-maintenance terrain plot. Each sample was fractionated and weighed across fresh, air-dried, and oven-dried states. Results demonstrated that total biomass, particularly for the fresh weight equation, exhibited greater performance across all log positions compared to air-dry weight and oven-dry weight equations. Using Newton’s formula as a volumetric benchmark, error analyses (Mean Bias Error, Root Mean Square Error, and Standard Deviation) confirmed the reliability of Smalian’s, Huber’s, and Bruce’s formulas, with Huber’s method consistently exhibiting the lowest error across all evaluated metrics and log intervals. An estimated empirical form factor was determined to be 0.579, surpassing the previously reported values for older age classes (6-9 years). These findings provide reliable, site-specific allometric equations and form factors for early-age short-rotation plantations.