Soil Calculator

Calculating soil requirements relies on basic geometric and physical principles involving volume, mass, and density. First, the surface area is determined by multiplying length by width (Area = Length × Width). Next, the volume needed is found by multiplying this surface area by the desired depth of the soil bed (Volume = Area × Depth). To find out how heavy that soil will be, multiply the calculated volume by the soil's bulk density (Weight = Volume × Density). Finally, multiplying the total weight or volume by your local supplier's unit price yields your total estimated project cost.

Imagine you are building a new rectangular raised garden bed that is 10 feet long, 4 feet wide, and you want a soil depth of 0.5 feet (6 inches). First, calculate your area: 10 ft × 4 ft = 40 square feet. Second, calculate the volume needed: 40 sq ft × 0.5 ft = 20 cubic feet of soil. If you are purchasing a standard topsoil with an average density of 90 pounds per cubic foot, your total weight needed is 20 cu ft × 90 lbs/cu ft = 1,800 pounds. If topsoil costs $0.05 per pound, your total cost will be 1,800 lbs × $0.05 = $90.00.

Always buy 10% to 15% extra soil to account for settling, compaction, and uneven ground contours. Measure your depths in multiple places across the installation site to ensure an accurate average depth. Keep in mind that wet soil is significantly heavier and denser than dry soil, which can impact both your structural weight limits (especially on rooftop gardens) and your delivery transportation logistics.