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What "Dirt" Actually Means

Dirt is excavated earth: a natural mix of clay, sand, silt, and small rock dug from below the surface. Unlike topsoil, it contains very little organic matter, which is exactly why builders like it. It does not decompose, shrink, or shift the way rich garden soil does, so it holds grade for years under lawns, patios, and foundations. The trade-off is that almost nothing grows well in it. Plan to use dirt for structure and volume, then cap any planting surface with 4 to 6 inches of topsoil.

The Formula: Why You Divide by 27

Every dirt calculation follows the same three steps. First, multiply length by width by depth, all in feet, to get cubic feet. Second, divide by 27, because one cubic yard is a cube 3 feet on each side, and 3 × 3 × 3 = 27 cubic feet. Third, add your compaction allowance. Worked example: a 20 by 10 foot area at 6 inches (0.5 feet) deep is 20 × 10 × 0.5 = 100 cubic feet, and 100 ÷ 27 = 3.7 cubic yards. Add 15 percent for compaction and you order about 4.25 cubic yards. The dirt calculator above runs exactly this math, including the weight conversion at 1.15 tons per cubic yard.

Loose, Bank, and Compacted Volume

The same dirt takes up a different amount of space depending on its state. Dirt sitting undisturbed in the ground is called bank volume. Once dug, it fluffs up with air pockets and grows by roughly 20 to 25 percent: that is loose volume, the state it is in when the truck dumps it. Spread, wetted, and rolled, it settles back down and loses 10 to 20 percent of its loose volume in the process. This is why a hole that measures exactly 10 cubic yards can swallow 12 yards of delivered dirt. The calculator result is finished, in-place volume, so always add the compaction percentage before ordering.

Choosing Between Raw, Screened, and Topsoil

Raw dirt at $8 to $15 per cubic yard is the cheapest way to add bulk: raising grade, filling old pool holes, and building up low spots. It may contain rocks and clods, which is fine below the surface. Screened dirt at $18 to $35 per yard has been passed through a mesh that removes debris larger than about half an inch, so it spreads smoothly and is the right choice for the finish layer of a grading job. Neither type grows plants well. Wherever grass or garden beds will sit on top of your dirt work, finish with 4 to 6 inches of screened topsoil and calculate that layer separately with the topsoil calculator.