In conventionally designed bridges, the inelastic displacement is estimated using an amplification factor (R_d) suggested by AASHTO which was developed based on Single-Degree-of-Freedom system. This study models the nonlinear behavior in different components of bridge and presents an equation of inelastic displacement ratio, C_μ, that can better predict the inelastic displacement. While AASHTO R_d closely matches C_μ corresponding to average response of different earthquakes, it does not give a reliable estimation for a wide range of earthquakes. Two equations are developed based on mean + standard deviation (SD) and mean + 3×SD to incorporate the variability in C_μ due to dynamic nature of bridge and wide range of earthquake. Additionally, it examines the influence of connection of columns to the ground, column height, deck width, number of spans, and damping ratio on C_μ. Contrary to AASHTO suggestion, C_μ was found to be increasing with increase in damping ratio.