The tree volume equations for Eucalyptus plantations are essential to estimate productivity, generalize equations that consider different genotypes and water regimes with low bias, and simplify plantation management. Our study evaluated the possibility of a generalized tree volume equation for eight Eucalyptus genotypes under contrasting irrigation regimens. We evaluated a seven-year-old plantation with E. nitens, E. badjensis, E. smithii, E. camaldulensis x globulus and two varieties of low and high productivity of E. globulus and E. nitens x globulus genotypes in two contrasting irrigation regiments (summer irrigated vs. no irrigated conditions). Diameter (DBH) and total height (H) measurements were considered in tree equations (Schumacher and Hall (1933), Honer (1967) and Clutter et al. (1978)). Then, the best volume equation was selected from the adjusted coefficient of determination, mean square error, and AIC and BIC parameters. Finally, the validation was carried out with the Jackknife method. The results showed that it is possible to use a generalized tree volume equation; the genotype, irrigation regime and their interaction were not statistically significant for all equations. The best tree volume equation was Schumacher and Hall (1933), which showed the best fit and minor bias, with a little trend to underestimate volume (total and merchantable) in trees with a volume greater than 0.22 m³. These results suggest that it is possible to use a generalized tree volume equation that would simplify plantation productivity projections while maintaining a good fit and low bias.