This paper presents a novel and simplified method to predict the damping ratio and power output of a cantilever-based electromagnetic vibration energy harvester through finite element analysis. A strong relationship was determined between the mechanical damping of a structure and the resonant stress at the clamped end of the structure under critically damped condition, otherwise described as the critically damped stress. This relation was used as a basis to develop a material-specific damping stress equation. The equation was then integrated into FEA to analyse a certain electromagnetic vibration energy harvester design by considering the variation in damping and power output for every structural change. The effect of the phase difference on the power output of the electromagnetic harvester was also considered. The FEA design that recorded the highest power output prediction (11.1% higher than the initial structure) was then verified experimentally, displaying a good agreement with experimental results, recording an error of less than 5.0% for the amplitude and voltage evaluation and 8.0% for the power output assessment. Hence, this validates the accuracy of the proposed method in predicting not only the mechanical damping of regular cantilever beams, but also other cantilever beam-based structures.