Soil Calculator

Pick rectangular, set length 8 ft, width 4 ft, and the depth you actually want filled. A typical 12 in depth gives 32 cu ft, which is roughly 1.2 cubic yards. At the default 1.5 cu ft bag size, that is 22 bags of garden soil, or one small truck delivery if you order in bulk. Most veggie beds need at least 10 to 12 in of soil for healthy root growth, so do not skimp on depth when you size your order.

Density depends on how much organic matter, air, and water each mix holds. The calculator uses common landscape-supply values: potting mix is the lightest at about 50 lb per cu ft because peat and perlite are airy; garden soil sits around 75 lb per cu ft as a blend of topsoil, compost, and amendments; compost is around 80 lb per cu ft; topsoil is about 90 lb per cu ft because it is mostly mineral soil; sand is the heaviest at roughly 100 lb per cu ft. A 32 cu ft bed weighs about 1,600 lb of potting mix but close to 3,200 lb of sand, which is why most raised beds use a lighter blend.

Potting mix is a soilless blend of peat or coco coir, perlite, vermiculite, and slow-release fertilizer, designed for containers where drainage and weight matter. Garden soil is a heavier blend of topsoil and organic matter intended for in-ground beds and raised beds, where it can settle and compact without choking roots. Use potting mix in any pot, planter, or window box; use garden soil in raised beds and in-ground gardens. Mixing the two (about 1 part potting mix to 3 parts garden soil) is a common trick for deep raised beds that need both structure and air.

One cubic yard equals 27 cubic feet, so divide cubic feet by 27 to get cubic yards. For bags, divide cubic feet by the bag size printed on the label: a 1.5 cu ft bag is the most common US size, so 30 cu ft of soil rounds up to 20 bags. The calculator rounds the bag count up because a partial bag is still a full purchase, and ordering an extra bag costs less than stopping a project to drive back to the garden center.

Not always. For beds deeper than about 18 in, the hugelkultur or lasagna method works well: fill the bottom third with logs, sticks, leaves, or grass clippings, then top with 10 to 12 in of garden soil. That cuts soil cost, retains moisture, and adds slow-release nutrients as the bottom layer breaks down. If you are growing root vegetables, keep the soil layer at least 12 in deep over the fill. Use the custom volume mode in the calculator to enter just the soil layer in cubic feet.