<p>Based on an inventory of 69 dams formed by rock slope failures in southwestern Norway and published landslide dam inventories from other parts of the World we developed semi-empirical relationships linking the maximum dam height (<i>H</i><sub>D.max</sub> in m) to dam volume (<i>V</i><sub>D</sub> in 10<sup>6</sup> m<sup>3</sup>) and other relevant parameters such as valley width (<i>W</i><sub>V</sub> in m) or dam area (<i>A</i><sub>D</sub> in km<sup>2</sup>). Power-laws are obtained for <i>H</i><sub>D.max</sub> = <i>f</i>(<i>V</i><sub>D</sub>) and <i>H</i><sub>D.max</sub> = <i>f</i>(<i>V</i><sub>D</sub>, <i>W</i><sub>V</sub>), while a linear relationship links <i>H</i><sub>D.max</sub> to the ratio <i>V</i><sub>D</sub> / <i>A</i><sub>D</sub>. For dams in southwestern Norway, the linear relationship <i>H</i><sub>D.max</sub> = 1.75 × <i>V</i><sub>D</sub> / <i>A</i><sub>D</sub> has least uncertainties and provides best results when comparing predicted dam heights with a validation dataset composed of existing dams in northern Norway and numerically modelled dams for possible rock slope failures. To assess the stability of future dams we use the predicted dam heights in the dimensionless blockage index DBI and relating this index to the probability of dam failure derived from our dataset and other published databases on landslide dams. This study underlines the potential of semi-empirical relationships for assessing dam height and stability that needs to be included in preliminary hazard and risk assessment for unstable rock slopes, because damming of a river is an important secondary effect of landslides due to upstream flooding and possible outburst floods in case of dam failure.</p>