A model describing the average rate of energy dissipation in random waves breaking in shallow water, published previously by the first author and Janssen (1978), has been applied to an extensive set of data for the purposes of calibration and verification. Both laboratory and field data were used, obtained on beaches with a more or less plane slope as well as on barred beaches, and for a wide range of wave conditions. Optimal values have been estimated for an adjustable breaking waveheight-coefficient in the model; these appear to vary slightly but systematically with the incident wave steepness, in a range which is physically realistic. A parameterization of this dependence allows the use of the model for prediction. Applied to the present data set, the correlation coefficient between measured and predicted rms wave heights is 0.98, with an rms normalized error of 6% and a bias which does not differ significantly from zero.