I started my business in May 03. One of my first opportunities in this business was a mulch job. I was in the same boat...how much mulch do you need. In my case I connected with a lawn & garden shop that was more than willing to help with any question I had, after all you become their customer. I was told the following, as a general rule 2 scoops* of mulch will cover approximately 100 square feet 3 inches deep. Of course the question is, how big is the scoop that is being used? In my case it was approx. 6 feet long, sorry I cannot tell you exactly how much was in a scoop. Here is another way of figuring it, I can get 3 scoops in a 4x8 utility trailer without worrying about the axel.
Hope this helps you out. Keep reading, research the threads, just about every question I could think of has been answered here. This is a great place to get information, read, read, read.
Can't we all just get a lawn?
CUTTING EDGE LAWN SERVICE
MOWING THE EARTH ONE YARD AT A TIME