Coastal structures play a major role in protecting people and property given the increasing threat of climate-change-induced flooding. Hence, an accurate prediction of wave overtopping for each structure is required to protect both people and properties on the structure's lee side. In this study, a formula set is developed for predicting the mean wave overtopping rate for vertical and slightly battered smooth impermeable structures. The formula set is derived using available datasets of small-scale laboratory experiments and further validated using large-scale laboratory and prototype tests and field measurements. The developed formula set for vertical structures is simple, physically sound, and contains consistent functional forms for deep and shallow water conditions, making it unique among other existing formulas. More importantly, its performance based on several accuracy metrics, is superior to existing prediction methods, including over a wide range of environmental conditions and structural characteristics. Correction factors are proposed for applications to slightly battered structures, as well as obliquely attacking waves. Finally, the formula for probabilistic design is also suggested to account for safety margins in practical applications.