In this paper, practical yet accurate formulae are proposed to predict the structural damage of rectangular unstiffened and stiffened plates under explosion loads. The numerical computation method adopted in this study was validated using published test data and then, rigorous parametric studies were conducted for various plate models. Regression analyses of the parametric study results were performed to derive design formulae, which produced linear relationships between the residual damages of plates and an impact parameter. These formulae have been compared with existing ones and it is confirmed that the proposed ones are more accurate and simpler than others.