A vertical wall with an overhanging horizontal cantilever slab was tested in a small-scale test setup (with a scale of 1:20) under wave impact (impulsive) loads. A single breaking wave creates two distinct sequential impacts on the vertical and horizontal parts of the cantilever. The breaking wave jet hits on the vertical wall then rises with an uprush jet velocity and creates the second impact on the horizontal cantilever. This upward water momentum depends on the uprush jet velocity. In this study, data from pressure sensors was used to analyze the average uprush jet velocity (u(v_av)) under regular breaking waves. A formula to predict the average uprush jet velocity on a vertical structure is proposed. Wave height at the toe of the foreshore (H-1), water depth at the structure toe (h(s)), and wave period (T) were found to be the main parameters governing the average uprush jet velocity. In addition, the influence of geometric properties such as clearance between still water level and horizontal part of the cantilever (c') were analyzed. The proposed formula is applicable within the range 0.45 <= H-1/h(s)<= 1. 2, 2. 0 s <= T <= 2. 8 s and 0. 75 m <= h(s)<= 1. 65 m.