A Conversion formulas were studied for estimating statistical-based representative wave heights (the mean wave height (Hm), root-mean-square wave height (Hrms), average of the highest one-third wave height (H1/3) and average of the highest one-tenth wave height (H1/10)) from the zeroth moment of the wave spectrum (m0). The applicability of five sets of existing conversion formulas was examined based on two field experiments of the COAST3D project (using 13,430 wave records). The examination showed that the conversion formulas derived from the Weibull distribution with a constant shape parameter gave the best prediction. The best set of conversion formulas was modified by reformulating the shape parameter in the formulas. The modified formulas gave slightly better predictions at Hm, Hrms and H1/3, and considerably better prediction at H1/10 than those of existing formulas. The modified formulas can be applied from shallow water to deepwater