Calculate soil from a few simple inputs in the United States.
Filling a bed needs volume, and it needs more volume than the raw dimensions suggest. Area times depth (with the depth converted from inches to feet) gives the finished cubic footage, but a fresh soil blend compacts once watered and worked, so a settling allowance of 10 to 20 percent is added before you order. Dividing by 27 converts to the cubic yards a bulk supplier sells in. The result is then split by your compost share, because good bed mix is not pure topsoil: roughly 60 to 70 percent screened topsoil with 30 to 40 percent compost gives structure and drainage plus the organic matter that holds nutrients and moisture.
Finished bed volume
finished cu ft = planting area (sq ft) x fill depth (in) / 12
Order volume with settling
order cu ft = finished cu ft x (1 + settling%)
Blend split
compost cu yd = total cu yd x compost%; topsoil = remainder
A freshly delivered blend is fluffy with air pockets. After the first few waterings it compacts, and a bed filled exactly to the rim drops an inch or two. Ordering 10 to 20 percent extra saves a second delivery fee for a small top-up.
For vegetable beds, roughly 60-70 percent screened topsoil to 30-40 percent compost works well. All-compost beds hold too much water, shrink dramatically as the organic matter mineralises, and can carry nutrient levels high enough to harm seedlings.
For beds deeper than about 12 inches, many gardeners fill the lower third with coarse organic material such as branches and leaves. Just remember most vegetables root in the top 8 to 12 inches, so keep that upper layer as proper blended soil.
In United States, imperial units are in everyday use.
Results on this page are expressed in USD (US Dollar). Figures are estimates for general planning — confirm current rates and thresholds with the relevant United States authority before relying on them.