Optimum design and location of wave energy converters in the marine environment require accurate assessments of the spatio-temporal variability of the available wave energy flux. However, numerical hindcast databases (commonly exploited for these long-term evaluations) integrate a restricted number of parameters such as the significant wave height Hs or the peak period Tp. Computation of wave power density from hindcast database is thus conducted by relying on simplified formulations derived from approximations of the group velocity and the wave energy spectrum. The present investigation quantified the biases in wave power computation from two standard formulations, based on the energy period and the peak period, respectively. The analysis relied on NOAA observations in 17 locations of the North-West Atlantic, the Gulf of Mexico and the Caribbean Sea. Whereas the energy-period formulation was a very good approximation of the wave power density in deep waters, the peak-period formulation (with a default calibration coefficient α=0.9) overestimated locally, by more than 8%, the available wave energy flux. A refined distribution of α against classes of Hs and Tp was established to reduce these differences, decreasing the relative difference from 9.9% to 0.3% off the Greater Antilles.