A way of measuring the density or stocking in a forest stand based on the well-known dynamics of how individual trees grow and stands develop. The basic principle is that the bigger the tree, the more site resources the tree needs to survive. The scale for relative density ranges from to 0 to 100 and the scale applies to stands of all sizes. Stands in the relative density range of 0 to 30 are more or less open and there is room for understory plants to grow. In the range from 30 to 55 stands approach "full stocking" and understory development is progressively suppressed. From 55 to 100 some trees in the stand must die before others can grow larger, and the understory is suppressed to non-existant. Classical old-growth stands with well-developed understories are either gappy or at a RD less than 30.