Mulch is any material spread over the soil surface to cover the ground, serving the dual purpose of landscape aesthetics and soil health. Because it is a three-dimensional product, determining the amount needed for a project requires understanding volume, not just area. Accurate measurement is the only way to ensure a landscaping project is completed efficiently, avoiding the cost and inconvenience of over-ordering or running short of material. This process relies on converting surface area and desired depth into a measurable volumetric unit.
Understanding Volume: Bagged vs. Bulk Mulch
Mulch is always measured and sold volumetrically. Smaller quantities, typically bought at garden centers, are sold in bags measured by the cubic foot. Standard bag sizes usually contain two cubic feet of material, which is ideal for small flower beds or touch-up work.
Larger landscaping projects require purchasing in bulk, which is measured in cubic yards. The cubic yard is a much larger unit of volume, containing exactly 27 cubic feet. Buying in bulk is often more economical for large areas, but it requires precise calculation to ensure the correct amount is delivered. Understanding this 27:1 ratio between cubic feet and cubic yards is the foundational step in successful material ordering.
The Standard Calculation Formula
Determining how much mulch to order involves a standardized calculation that combines the area of the bed and the desired application depth. The process begins with measuring the length and width of the area to be covered to determine the total square footage. This two-dimensional area must then be converted to a three-dimensional volume, which is why the desired depth is factored in.
To convert square feet and depth (in inches) into cubic yards, a specific constant is used. The simplest formula is to multiply the total square footage by the desired depth in inches, and then divide that result by 324. This constant, 324, is derived from the fact that one cubic yard covers 324 square feet at a uniform depth of one inch. For example, a bed measuring 100 square feet that needs a three-inch layer of mulch would require 0.92 cubic yards (100 3 / 324).
The result is the minimum volumetric amount required to cover the area. This calculation provides the precise quantity needed, allowing for an accurate order of bulk material or a simple conversion to the number of two-cubic-foot bags. For the example above, 0.92 cubic yards equates to approximately 12.4 bags, which should be rounded up to 13 bags for the purchase.
Real-World Adjustments for Accurate Ordering
Real-world factors necessitate making adjustments to the final quantity ordered. The most common recommended depth for general landscaping is between two and four inches, which balances weed suppression with allowing adequate air and water flow to the soil. Newly created beds or areas that have not been mulched for several years may require a deeper layer, closer to four or five inches, to establish an effective barrier.
The type of mulch material also affects the final volume needed due to compression and settling. Fine-textured materials, such as shredded bark, tend to compact more easily than coarser materials like wood chips or nuggets. This difference means the initial volume of fine mulch may settle more quickly, potentially requiring a slightly larger initial order.
It is common practice to add a small percentage to the calculated total to account for unavoidable factors like uneven spreading, spillage during application, and natural settling. An adjustment of 5% to 10% above the calculated volume helps ensure complete coverage and prevents the need for a second, small delivery.