Bark, often referred to as mulch, is a layer of material applied to the surface of soil, providing multiple benefits. This organic layer aids in moisture retention by reducing water evaporation and suppresses the growth of unwanted weeds by blocking sunlight. Accurately calculating the precise volume required is necessary for a successful project. This article provides a step-by-step guide to determine the exact quantity of bark you need.
How to Measure Your Coverage Area
The first step in calculating your material needs is to determine the total surface area, or square footage, you plan to cover. For simple, rectangular or square planting beds, find the area by multiplying the length by the width, ensuring all measurements are taken in feet. For example, a bed 20 feet long and 5 feet wide has a surface area of 100 square feet. This standardized unit of measure simplifies the volume calculation later on.
Irregularly shaped areas, such as curved garden borders, require a different approach. Divide the complex shape into several smaller, manageable rectangles or squares. Calculate the square footage for each section individually using the length-by-width formula. Add the individual totals together to find the overall coverage area for your project.
Choosing the Right Mulch Depth
The application depth is a determining factor for both the material’s effectiveness and the total volume you will purchase. Applying the correct depth ensures the material performs its intended functions without causing harm to existing plant life. A layer that is too thin (less than 2 inches) will not effectively suppress weeds or retain soil moisture. Conversely, an excessive layer (over 4 inches) can suffocate plant roots by blocking the necessary exchange of air and water.
For maintaining existing beds or refreshing the look, a depth of 2 inches is usually adequate for aesthetic top-dressing. New planting beds or areas with aggressive weed growth benefit most from a 3-inch layer, which creates a more robust barrier against sprouting seeds. While a 4-inch depth can be used for heavy-duty coverage, it is the practical maximum to prevent problems like root suffocation and excessive moisture near plant crowns. Keep this measurement in inches, as it will be used directly in the final volume formula.
The Volume Calculation Formula
Once you have the total square footage and the desired depth in inches, calculate the volume in cubic yards, which is the industry standard for bulk purchasing. The standard formula is: (Area in square feet x Depth in inches) / 324 = Cubic Yards. This formula works because the constant, 324, represents the amount of square feet that one cubic yard of material will cover at a 1-inch depth.
The constant 324 is derived from the fact that one cubic yard contains 27 cubic feet of volume. Knowing that one cubic yard covers 324 square feet at a 1-inch depth simplifies the overall calculation significantly. For quick reference, one cubic yard covers 108 square feet at a 3-inch depth, and 81 square feet at a 4-inch depth.
Practical Tips for Ordering and Delivery
After calculating the cubic yard requirement, adjust the total to account for settling and compaction. Add an extra 5 to 10 percent to your final calculated volume. This ensures you have enough material to achieve the desired finished depth after settling.
While bulk material is sold in cubic yards, smaller projects may involve purchasing material in bags, which are typically sold by cubic feet. One cubic yard equals 27 cubic feet. A standard large bag usually contains 2 cubic feet, meaning you need approximately 13.5 bags per cubic yard. When arranging delivery, be sure to clearly specify a convenient, accessible location for the material to be dumped, as a single cubic yard of organic material can weigh hundreds of pounds.