This paper tests the quality of calculated 2D isovist variables as predictors of perceived landscape openness. An isovist is the calculated field of view from a given viewpoint in space. Three isovist variables were selected to estimate openness: the minimum radial, the maximum radial and the average radial. An experiment with 32 participants was conducted to compare values of these calculated variables with perceived openness. The comparison showed that two variables, the maximum radial and average radial, explained most of the variation of perceived openness for groups and individuals. The three calculated isovist variables were strongly correlated to their measured equivalents in the field, which were obtained with a binocular with a rangefinder. The isovist variables also showed strong correlations with their perceived equivalents obtained by the perception of the 32 participants, except at very long distances. This research shows that the selected isovist variables are good indicators for perceived landscape openness.