If planting more than one strata of vegetation, you should factor in the space occupied by larger, more widely spaced plant types when determining quantities of smaller types of vegetation. For example, if you plan to plant trees and shrubs, be sure to subtract the trees from the number of shrubs needed.
The page below performs this calculation for you. First enter the size of your planting area, then choose the desired planting density for each form of plant (note: o.c. = on center). Part 1 displays the quantities for trees, shrubs and groundcovers, assuming square grid spacing. Part 2 displays the quantity for emergents OR live stakes. This part works independently from the tree-shrub-groundcover calculations, because many emergent plantings consist solely of emergent species, and the same is true for live stake plantings. Emergent quantity is based on planting a clump of 4 plants per planting spot. Research shows that clumped plantings of emergents and graminoids survive better and establish cover more rapidly than evenly spaced plantings.
Click here for information on how to measure irregularly-shaped areas.