Many gardeners find the convenience and beauty of raised beds enhances the gardening experience and allows them to produce more crops in a smaller space. Construction consists of wooden or stone structures raised above the ground level that are designed to hold soil for planting flowers, herbs or vegetables. When it comes to filling the bed with soil, those new to raised beds face some confusion over how to calculate the amount of soil needed.
Measure the width, length and depth of the interior of the raised bed. Although measurement in inches may be suitable for small beds, measure beds larger than 3 feet by the foot. Round measurements up to the next foot.
Multiply the length by the width to find the surface area of the bed. For example, a 4-foot by 8-foot bed has a surface area of 32 square feet.
Multiply the surface area by the depth of the bed to find the volume of the raised bed in cubic feet. For example, a 1-foot deep bed with a surface area of 32 square feet has a volume of 32 cubic feet. A 2-foot deep bed with the same surface area has a volume of 64 cubic feet.
Divide the cubic feet by 3 to determine the number of cubic yards of soil you need. In the first example with the 32 cubic foot volume, the bed has a 10 and 2/3 cubic yard volume. Round this number up to the next number. To order enough soil to fill the bed in the example, you will need 11 cubic yards.
Visit your garden supply centre or local contractor to order the garden soil. Soil by the truckload is generally sold by the yard, which means a cubic yard. Smaller amounts may be sold in bricks or bags that indicate the area they will cover.
For more exact measurements convert inches and express as decimals when measuring in feet. For example, 2 feet 3 inches = 2.25 feet, 2 feet 6 inches = 2.5 feet, and 2 feet 9 inches = 2.75 feet.
Always overestimate to allow for variations in size. Leftover soil can be used for other projects, but not having enough can cause delays in planting or require extra trips to the supplier. If you are having soil delivered, this can be costly.