Garden Soil Volume Calculator

The short answer to 'how much soil for a 4x8 raised bed': at 12 inches deep you need 32 cubic feet of soil, which is 1.19 cubic yards. At 6 inches deep you need half that: 16 cubic feet (0.59 cubic yards). Our calculator above does the exact math for any bed size, adds a settling buffer, and converts the result into bag counts for common bag sizes.

Multiply length x width x depth, all in the same unit. A bed 8 ft long, 4 ft wide and 1 ft deep needs 8 x 4 x 1 = 32 cubic feet. For a round bed use pi x radius squared x depth. Divide cubic feet by 27 to get cubic yards, which is how bulk soil is sold. Add 10-15% extra because soil settles after watering.

One cubic yard equals exactly 27 cubic feet. Bulk soil, topsoil, mulch and compost are priced per cubic yard, while bagged products are labeled in cubic feet or quarts, so divide bag volume into 27 to compare. A 2-cubic-foot bag is 1/13.5 of a cubic yard.

Divide 27 by the bag size: 2-cubic-foot bags need 14 bags per cubic yard (13.5 rounded up), 1.5-cubic-foot bags need 18, and 3-cubic-foot bags need 9. The bag calculator above rounds up automatically and includes your settling buffer, so you never come up short mid-project. The same math converts cubic yards to bags for a mulch calculator too.

Compare price per cubic yard: multiply the bag price by 27 divided by the bag's cubic feet. A $6 bag of 2 cu ft soil costs $81 per cubic yard, so bulk soil at $45 per cubic yard wins for large projects. Bags usually win under about 0.5-1 cubic yard because bulk yards add a delivery fee. The bulk-vs-bag advisor above computes your exact breakeven point.

Mel's Mix is the square-foot-gardening soil recipe: one third coarse vermiculite, one third peat moss (or coco coir), and one third blended compost. For 32 cubic feet of bed volume you need 10.67 cubic feet of each component. The recipe mode above splits your bed volume into exact component amounts.

A classic economical raised bed mix: 60% topsoil, 30% compost, and 10% aeration material such as perlite, pumice, or coarse sand. For 32 cubic feet that is 19.2 cu ft topsoil, 9.6 cu ft compost, and 3.2 cu ft aeration. It is cheaper than bagged raised-bed mix and drains better than plain topsoil.

Hugelkultur fills deep beds bottom-up with woody layers that slowly decompose: roughly 40% logs and large wood, 15% branches and twigs, 10% leaves or straw, 5% grass clippings, then 15% compost and 15% topsoil on top. It cuts the amount of purchased soil dramatically for beds deeper than 18 inches. The hugelkultur estimator above sizes every layer from your bed volume.

Apply bark or wood mulch 2-4 inches deep (3 inches is the standard recommendation); 2 inches is enough for weed suppression around established plants. This bark mulch calculator uses length x width x depth like soil: a 10 ft x 10 ft bed at 3 inches needs 25 cubic feet, just under one cubic yard. As a mulch calculator for tree rings, use the round shape and keep the ring 2-3 inches deep, never piled against the trunk.

This potting soil calculator treats each pot as a cylinder: pi x radius squared x height. A 12-inch-diameter pot that is 12 inches tall holds about 0.78 cubic feet (roughly 5.8 gallons), and a 5-gallon nursery pot holds about 0.67 cubic feet. Potting mix is often sold in quarts: divide quarts by 25.71 to get cubic feet.

It depends on the material and moisture. Typical loose bulk densities: topsoil about 75 lb per cubic foot, raised bed mix about 65 lb, compost about 45 lb, potting mix about 25 lb, and shredded bark mulch about 20 lb. The calculator converts your volume to pounds and metric tonnes so you can plan hauling and delivery.

Yes. Freshly filled beds settle 10-15% after the first few waterings, so add a 10-15% buffer to your calculated volume. Mulch does not compact the same way, but a 5-10% buffer still covers uneven spreading. The waste/settle slider above applies the buffer to bag counts, weight, and cost automatically.

To work out how much topsoil you need, multiply area by depth: a 10 ft x 10 ft area at 3 inches deep needs 25 cubic feet (0.93 cubic yards). Example: 1.19 cubic yards x 27 x 75 / 2,204.62 = about 1.09 tonnes. The weight panel works as a topsoil calculator in tonnes, and does this conversion for all five materials.

Use pi x radius squared x depth. A 3-foot-diameter bed filled 12 inches deep needs about 7.07 cubic feet (0.26 cubic yards), which is four 2-cubic-foot bags. For a tree ring, calculate the outer circle and subtract the inner circle around the trunk. Select the round shape above and enter the diameter.

You can, but it is not ideal: straight topsoil compacts over time, drains poorly, and is low in organic matter. Mixing in 30% compost and 10% aeration material (the 60/30/10 recipe) gives better drainage, more nutrients, and less compaction. Pure compost alone also compacts and is expensive, which is why blends win.

A 4x8 ft bed at 12 inches deep (1.19 cubic yards) costs about $53 in bulk soil at $45 per cubic yard, versus $96 for sixteen $6 bags of 2 cu ft soil. Enter your local bulk price, bag price, and delivery fee in the cost advisor above to get exact totals and the breakeven volume where bulk becomes cheaper.