During the last two decades, DBSCAN (Density-Based Spatial Clustering of Applications with Noise) has been one of the most common clustering algorithms, that is also highly cited in the scientific literature. However, despite its strengths, DBSCAN has a shortcoming in parameter detection, which is done in interaction with the user, presenting some graphical representation of the data. This paper introduces a simple and effective method for automatically determining the input parameter of DBSCAN. The idea is based on a statistical technique for outlier detection, namely the empirical rule. This work also suggests a more accurate method for detecting the clusters that lie close to each other. Experimental results in comparison with the old method, together with the time complexity of the algorithm, which is the same as for the old algorithm, indicate that the proposed method is able to automatically determine the input parameter of DBSCAN quite reliably and efficiently.