Stocking relationships are an important tool for foresters because they provide a means for evaluating how effectively the trees in a stand use available growing space. While stocking guidelines are not available for many tropical tree species, readily obtained measurements of stem and crown diameters can be used to develop preliminary stocking guidelines for most tree species. We demonstrate this approach for the endemic Hawaiian hardwood, Acacia koa, a species of major ecological and economic value in Hawaii. Using data from repeated censuses of multiple sites, we evaluated the influence of site quality and stand age on stocking guidelines for A. koa. Our results demonstrated that A. koa required less canopy space for a given dbh on moist windward sites than on drier leeward sites. In addition, we showed that on the windward sites A. koa required relatively less crown space with increasing tree size, whereas on the leeward site the opposite pattern was found. Size-density data from permanent inventory plots at the leeward study site showed excellent correspondence with the stocking guideline derived from the stem-crown diameter allometry. These stocking guidelines can be used to guide the establishment of new A. koa stands or to develop thinning regimes where information from spacing and thinning trials is not available and until better information is available.