Determine the number of square feet to be mulched.

For a depth of 2" thick, divide the square footage by 6
For a depth of 3" thick, divide the square footage by 4
For a depth of 4" thick, divide the square footage by 3

Then divide that number by 27 in order to arrive at the number of cubic yards needed to cover your square foot area. (because there are 27 cubic feet in a cubic yard.)

Example: 500 sq. feet of area to be covered with a 3" layer of mulch.
500 divided by 4 = 125
125 divided by 27 = 4.63 cubic yards (rounded off to 5 yards)

One Yard Covers

At a depth of 1/2" .......... 550 square feet
At a depth of 1" ............... 275 suare feet
At a depth of 2" .............. 130 square feet
At a depth of 3" ................ 70 square feet
At a depth of 6" ................ 45 square feet
At a depth of 12" .............. 20 square feet