Mulch is used as an additive or supplement to gardens, as a barrier against weeds and as a cooling and water conservation agent for plants. Purchasing the correct amount of mulch requires estimating the coverage area. This is important so as not to make the mulch bed too deep, causing moisture issues, or too shallow, causing ineffective coverage. Determining the right amount of mulch is achieved using various calculations to find the proper needs.
Mulch is sold by the cubic yard to make it easier for distribution. Since the land the mulch will be applied on is measured in square feet, various calculations must be performed to determine the amount of mulch required to cover the area. These calculations provide the best estimate so that the least amount of excess occurs without the need to purchase more mulch to finish the job.
Before doing any calculations, certain measurements must be found to create the numbers required for the calculations. The square feet of the area must be determined first. This is achieved by measuring the longest and widest sides of the area. For straight-sided areas this is a two-measurement process; for irregular areas this will create a close estimate of the square footage. Circular areas are found by determining the radius of the area, which is the distance from the center to the outside edge of the circle.
The method of calculation is a combination of multiplication and division. For regular-shaped areas the length and width of the area are multiplied together to find the total square feet. For irregular-shaped areas the longest length is multiplied by the longest width to find the square footage. For circular areas, multiply the radius by 2 to find the total diameter of the area; then multiply by pi, which is 3.14, to find the total square feet within the circle.
Since mulch is sold by cubic yard, the total square feet must be converted to fit the measurement. One cubic yard is equal to 27 cubic feet, with the measurements for a yard being 3 by 3 by 3 feet. One cubic foot is measured at 1 by 1 by 1 foot. Multiply the total square feet by the depth required for the mulch; depth is expressed in feet or fractions thereof. Convert any fractions into decimals for calculation. This will provide the amount of cubic feet. From there you can determine the cubic yards.
Measurements vary for different types of mulch. These measurements are determined by various factors such as whether the mulch comes in bulk, bag or bale. Wood mulch is sold either by bulk or cubic-foot bags of 2 or 3 cubic feet. Pinestraw and wheat straw are sold by the bale with pinestraw requiring more material per square foot. Pea gravel is sold per 50-pound bags, which covers 7 square feet each.