Find the area to cover
First of all, calculate the widest and longest portions of the area to be covered. This will be an easy and good process if the plant bed is straight sided. On the other hand, know that the irregular beds will be near to the exact measurement if calculated from the ends of the widest and longest sides. Therefore, find the length and width in feet of a rectangle or square that has to be mulched. Multiply the width times the length and you will get the area in square feet.
Calculate across the widest part of the circle to be mulched and divide that by two. Then multiply the number by itself. For instance, if it is 16 feet across, dividing it by 2 you will get 8. Eight times 8 is 64. After that, multiply this number by pi which is 3.14 and it provide you the area of the circle in square feet. Moreover, calculate the height of a triangle with same sides to be mulched. Multiply the base with the height and divide by two. This will give you the area of the triangle in square feet.
Calculating the amount of mulch
See what kind of mulch you will need, and how much do you want it. Mulches such as cocoa hulls should be used at a depth of just 1 inch and in the case of wood chips should be used to a depth of 2 to 4 inches. Multiply the total square feet area by the depth in inches that you require the mulch to be. Then divide by 324 square feet that is 1 cubic yard 1 inch deep. It will give you the number of cubic yards you will require for your property.