How we calculate
Every number on DirtMath comes from a stated formula and a stated density or coverage rate. Nothing is hidden behind a black box, and nothing is reproduced from a proprietary table. If a figure below does not match your supplier, use theirs — regional material varies.
The formulas
- Area. Rectangle = length × width. Circle = π × (diameter ÷ 2)². Triangle = (base × height) ÷ 2. Multiple zones are summed.
- Volume. Cubic feet = area (sq ft) × depth (in) ÷ 12. Cubic yards = cubic feet ÷ 27.
- Weight. Tons = cubic yards × density (lb per cubic yard) ÷ 2,000.
- Bags and units. Count = total ÷ the capacity or coverage of one unit, rounded up, after your waste allowance is applied.
- Cost. Quantity × the price you enter. We do not fetch live prices; defaults are rough national midpoints for orientation only.
Densities and coverage rates
| Material | Value used | Note |
|---|---|---|
| Mulch | 800 lb/yd³ | Density of 800 lb/yd³ reflects typical dry shredded hardwood bark. Wet or composted mulch is heavier. |
| Topsoil | 2,200 lb/yd³ | Density of 2,200 lb/yd³ is typical for screened, moist topsoil. Sandy mixes are lighter; clay soils heavier. |
| Gravel | 2,800 lb/yd³ | Density of 2,800 lb/yd³ covers most crushed limestone and #57 stone. Pea gravel is slightly lighter at about 2,700 lb/yd³. |
| Sand | 2,700 lb/yd³ | Density of 2,700 lb/yd³ represents dry washed masonry sand. Wet sand weighs more per yard. |
| River rock | 2,800 lb/yd³ | Density of 2,800 lb/yd³ is typical for 1–2 inch washed river stone. |
| Sod | Roll (16" × 48") = 10 sq ft; Pallet (450 sq ft) = 450 sq ft | Roll and pallet coverage follow the most common US grower sizes; regional sizes vary. |
| Grass seed | New lawn (1 lb per 250 sq ft) = 250 sq ft; Overseeding (1 lb per 500 sq ft) = 500 sq ft | Rates reflect typical cool-season blends (tall fescue, perennial ryegrass). Always check the seed label. |
| Compost | 1,100 lb/yd³ | Density of 1,100 lb/yd³ reflects finished, moist yard-waste compost. Manure-based blends are heavier. |
| Pavers | 12" × 12" (1.00 sq ft) = 1 sq ft; 16" × 16" (1.78 sq ft) = 1.78 sq ft; 6" × 9" holland (0.375 sq ft) = 0.375 sq ft; 4" × 8" brick (0.222 sq ft) = 0.222 sq ft | Coverage figures are nominal face dimensions; actual pavers include a small joint allowance. |
| Retaining wall block | 6" H × 16" W (0.67 sq ft face) = 0.667 sq ft; 4" H × 12" W (0.33 sq ft face) = 0.333 sq ft; 8" H × 18" W (1.00 sq ft face) = 1 sq ft | Face dimensions follow the most common segmental wall block sizes sold in the US. |
| Rubber mulch | 1,200 lb/yd³ | Density of 1,200 lb/yd³ is typical for shredded recycled tire mulch. |
| Pine straw | Standard bale (50 sq ft) = 50 sq ft; Large / long-needle bale (70 sq ft) = 70 sq ft | Bale coverage varies by supplier and needle length; 50 sq ft is the common US standard bale. |
| Cubic Yards | 2,000 lb/yd³ | Conversions are exact geometry (27 cubic feet per cubic yard). The 2,000 lb/yd³ default weight is a mid-range figure for mixed landscape material. |
| Stone | 2,800 lb/yd³ | 2,800 lb/yd³ is a common figure for dry 3/4-inch crushed limestone. Granite and trap rock run heavier; lava rock far lighter. |
| Dirt | 2,400 lb/yd³ | 2,400 lb/yd³ represents typical moist unscreened fill. Clay-heavy dirt is heavier; sandy dirt lighter. |
| Pea Gravel | 2,700 lb/yd³ | 2,700 lb/yd³ is typical for dry rounded 3/8-inch pea gravel. Wet gravel weighs roughly 5 percent more. |
| Fill Dirt | 2,600 lb/yd³ | 2,600 lb/yd³ reflects typical moist unscreened fill dirt. Verify tonnage with your supplier's scale ticket. |
| Sq Ft to Cubic Yards | 2,000 lb/yd³ | Pure unit geometry: 1 cubic yard = 27 cubic feet, 1 inch = 1/12 foot. No material assumptions beyond the optional weight estimate. |
What these numbers are not
They are estimates for planning and ordering, not engineering specifications. Compaction, moisture, stone size and settling all shift real-world quantities by five to fifteen percent. For structural work — retaining walls over three feet, driveway bases, drainage design — follow your local code and, where required, a licensed professional.
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