Bridges are critical infrastructures subjected to dynamic and repetitive loads over extended periods, necessitating continuous monitoring to ensure their structural integrity. Monitoring the performance of a bridge involves several key parameters, with maximum deflection being of utmost importance. This study aims to develop an equation model using multiple regression analysis to establish the relationship between deflection values and rotation values obtained from a PCI girder bridge as a project case study. A 3-D Finite Element Method model was developed to accurately represent the bridge’s geometric and mechanical properties. Actual data on maximum deflection and rotation were acquired by subjecting the FEM model to realistic load conditions. Regression analysis was conducted to derive equations for calculating maximum deflection based on the measured rotation and strain data. The accuracy of the estimated maximum deflection was validated by comparing it with values obtained from 3D structural analysis using FEM software The results demonstrate that the proposed regression equation accurately estimates the maximum deflection, with an average accuracy rate of 98.185%. Thus, this method presents a reliable approach for estimating the maximum deflection based on tiltmeter readings, offering a practical solution with a commendable level of accuracy.