The amount of mulch needed to cover a garden area depends on the texture and density of the mulch material. Over time, the mulch settles, compacts and decomposes. One cubic yard of mulch equals 27 cubic feet.
Robert Black, Edward Gilman, Gary Knox and Kathleen Rupert, horticultural expert contributors to "Your Florida Landscape" mention that mulches are maintained between 2 to 4 inches in depth. Small-particle mulches like sawdust need to be maintained between 2 to 3 inches in depth after settling, while coarse mulch materials, such as shredded bark, are maintained up to 4 inches in depth.
Based on mathematical explanations in "Your Florida Landscape," the depth of the mulch layer determines how much soil area a cubic yard of mulch covers. If applied in a 4-inch layer, 1 cubic yard covers 81 square feet. Scattered at a depth of 3 inches, a cubic yard of mulch covers 108 square feet, and a 2-inch layer covers 135 square feet.
Instead of buying mulch in loose, cubic yard form from a landscape supply company, investigate the cost of bagged mulch. Bagged materials are sold in units or 1 to 2 cubic feet in size. For small projects, bagged mulch is easier to handle and excess bags usually are returnable for refund. Bulk, loose mulch sold by the cubic yard is not returnable, and excess material warrants storage in a pile out of sight.