In the assessment of earthquake performance of structures, maximum displacement demand is considered as the main parameter. Inelastic displacement ratio is used in earthquake engineering for obtaining estimates of maximum displacement demand. Inelastic displacement ratio is defined as the ratio of peak inelastic displacement to the peak displacement of the equivalent linear elastic system. Aim of this work is to assess the level of sensitivity of the displacement ratio to soil-structure interaction effects. Displacement ratios for equivalent nonlinear single-degree-of-freedom systems located at sites with sandy soil conditions are investigated in this study. The "Beam-on Nonlinear-Winkler-Foundation" (BNWF) model is utilized to represent the effects of soil-structure interaction on the dynamic response. Seismic response of a range of systems that represent various super-structure and soil conditions, were computed by means of nonlinear time history analysis. In total, 10'800 analyzes were carried out using 54 records for capturing the ground motion record variability. For the systems with short vibration periods (T< 0,6s) and high strength reduction coefficients (R> 3), it is observed that the displacement ratio is sensitive to the bearing capacity of the soil. It was observed that the displacement ratios are greater for the systems built on soils with low bearing capacity, compared to those on soils with high bearing capacity. Resulting displacement ratios are compared against those that are obtained using the existing methods.