In the present study, a data processing technique was introduced to develop a closed form shape empirical formulation in predicting ultimate strength of structures. The proposed method was verified by applying a ship's stiffened panel as an applied example. In particular, a refined empirical formulation in predicting the ultimate strength of stiffened panel subjected to longitudinal compression was proposed. Recently, Kim et al. (2017) observed that the ultimate strength behaviours fluctuated in small value of column slenderness ratio and urged the need for a more accurate empirical formulation. In order for an accurate ultimate strength behaviour of stiffened panel to be obtained, a total of 10,500 cases of numerical simulation results using the ANSYS Finite Element Method (FEM) were employed by considering the relevant size change of stiffened panels including plate thickness, web thickness, flange thickness, height of web, and breadth of flange. The simulation results were processed, in the case of initial imperfection, only for average level of initial deflection to plate. On the other hand, initial distortion to stiffener elements and no residual stress by welding were considered in this study. A detailed data processing technique and detailed modelling procedures, i.e, the scenario selection, FE modelling, FE analysis, were documented. From the obtained data processing results by this study, we have found that four (4) important parameters, i.e., P1=λ,P2=β,P3=hw/twandP4=Ipz/Isz are to be considered for the formulation of empirical formulation in predicting ultimate strength of stiffened panel under longitudinal compression (�xu/�Yeq). The proposed new empirical formulation revealed positive agreement with ANSYS FEM results (R2 = 0.98 for overall case). © 2019 Elsevier Ltd