The purpose of this work is to develop and validate an analytical model that provides accurate predictions of the mechanical properties of hollow box beams, in comparison to traditional methods. The study focuses on numerical results obtained for a hollow box beam with a rectangular cross-section. To achieve this objective, a novel analytical model was created. A finite element model (FEM) of the box beam was built in the comercial FEM software ANSYS Mechanical ADPL, and the results were compared using classical theory, the new equation, and numerical techniques. Linear static analysis was performed to analyze the results, and a mathematical method was employed to compare the outcomes. Validation of the newly developed equation was performed by comparing it with both the numerical model and the classical equation, and this approach proved successful. It was shown that the new equation outperforms the classical equation in accurately predicting the mechanical behavior of the studied geometries. This superiority was demonstrated through error analysis, which revealed that the new equation resulted in lower errors than the classical equation. It was found that the maximum error between the analytical equation and the numerical method decreased from approximately 2.5% for the classical equation to around 0.24% using the derived equation.