Step By Step: Calculate Mulch Needs - Landscape Management

When it comes to mulch, having too much can be just as bad as not having enough. By using a few simple charts and equations, contractors can determine how many cubic feet of mulch they need for jobs with beds of any shape and size. The same equations also will work to calculate needs for other materials, such as topsoil and stone.

Example 1: Rectangular Beds

You have a rectangular bed that measures 16 feet long by 10 feet wide and you want to lay mulch 3 inches deep. Multiply the bed’s length and width to determine the square footage. Divide the square footage by the conversion chart figure that corresponds to a 3-inch depth to convert square feet to cubic yards.

Calculations: 16 feet x 10 feet = 160 square feet 160 square feet/108 (chart figure) = 1.5 cubic yards of mulch

Example 2: Triangular Beds

You have a triangular bed with a height of 40 feet and a base of 10 feet. You want to lay mulch 4 inches deep. Multiply the bed’s base and height and then divide by 2 to determine the square footage. Divide the square footage by the conversion chart figure that corresponds to a 4-inch depth to convert square feet to cubic yards.

Calculations: (40 feet x 10 feet)/2 = 200 square feet 200 square feet/81 (chart figure) = 2.5 cubic yards of mulch

Example 3: Circular Beds

You have a circular bed that measures 30 feet across (15-foot radius). You want to lay mulch 3 inches deep. Multiply the bed’s radius (which is half of the distance of the bed’s diameter) by itself by 3.14 (pi–the ratio of the circumference of a circle to its diameter) to determine the square footage. Divide the square footage by the conversion chart figure that corresponds to a 3-inch depth to convert square feet to cubic yards.

Calculations: 15 feet x 15 feet x 3.14 = 706.5 square feet 706.5 square feet/108 (chart figure) = 6.5 cubic yards

Example 4: Irregular Beds

To calculate the amount of mulch needed for irregularly-shaped beds, divide them into smaller, workable shapes. For example, the beds throughout a client’s landscape can be broken up into three rectangles, one triangle and one circle, and you want to lay mulch 2 inches deep. Assign each area a letter. Using the appropriate equation for the bed’s shape, measure each area in feet and calculate the square footage. Add the square footage of each area together to determine the landscape’s total square footage. Divide the total square footage by the conversion chart figure that corresponds to a 2-inch depth to convert square feet to cubic yards.

Calculations: Triangular Area A: (15 feet x 20 feet)/2 = 150 square feet Rectangular Area B: 4 feet x 20 feet = 80 square feet Rectangular Area C: 6 feet x 20 feet = 120 square feet Rectangular Area D: 18 feet x 20 feet = 360 square feet Circular Area E: 10 feet x 10 feet x 3.14 = 314 square feet 150 square feet + 80 square feet + 120 square feet + 360 square feet + 314 square feet = 1,024 total square feet 1,024 square feet/162 (chart figure) = 6.3 cubic yards

Source: Kalamazoo Landscape Supply

illustrations: David Preiss