I have seen all the formulas and threads on calculating how much mulch is needed for a given size. What I do not see is how you take into account the number of plants that take up space in the bed. I recently estimated a bed based on size alone and came up with 36 yards. When I was speaking with the homeowner they indicated in the past it took between 15 and 18 yards. Luckily I never told them what my calculations indicated. Any help would be greatly appreciated.