How to Calculate How Much Dirt You Need
Measure the length and width of the area in feet and choose a depth for the job. Multiply length × width × depth (with the depth in feet) and divide by 27 to get cubic yards. Fill that will be compacted needs a compaction allowance on top. Then round up to the next half yard when you order.
Rather skip the arithmetic? The cubic yard calculator does it for soil, topsoil and garden beds, and the fill dirt calculator does it for holes, trenches and grading, with the compaction allowance built in.
The two formulas
A cubic yard is 27 cubic feet (3 ft × 3 ft × 3 ft), so either of these gives the same answer:
- Cubic yards = length (ft) × width (ft) × depth (ft) ÷ 27
- Cubic yards = area (sq ft) × depth (in) ÷ 324, because one cubic yard spread 1 inch deep covers 27 × 12 = 324 square feet.
Convert inches to feet by dividing by 12: 6 inches is 0.5 ft and 4 inches is 0.33 ft.
Step 1: Measure the area
- Rectangles and squares: length × width, in feet.
- Circles: measure straight across the middle (the diameter). The area is 3.1416 × (diameter ÷ 2)². The circle calculator does this for round beds and rings around trees.
- Triangles: ½ × base × height. If you only have the three side lengths, the triangle calculator works from those.
- Irregular shapes: split the area into rectangles, circles and triangles, work out each one and add them together. For a long curving bed, measure its length and its width at several points, and use the average width.
Step 2: Choose the depth for the job
| Project | Depth | Why |
|---|---|---|
| Top-dressing a lawn with compost | 1–2 in | Thicker layers can smother an established lawn. |
| Garden beds and raised beds | 6–12 in | Match to the root depth of what you are planting. |
| Fill and grading | As measured | The depth you are filling or raising, from the bottom to the finished grade. Across an uneven low spot, measure at several points and use the average. |
The coverage chart shows how far a cubic yard goes at each depth.
Step 3: Convert to cubic yards
Multiply the area by the depth in feet to get cubic feet, then divide by 27. Or multiply the area in square feet by the depth in inches and divide by 324. For most beds and lawns, add 5–10% for uneven ground, settling and spills.
Step 4: Add a compaction allowance for fill dirt
Fill dirt is delivered loose, and loose soil shrinks when it is packed down. To fill a measured space and compact it, you need more loose cubic yards than the space measures:
- Loose fill to order = space to fill (yd³) × (1 + compaction allowance)
| How the fill is placed | Allowance |
|---|---|
| Sand or gravel, compacted in layers | 17% |
| Loam (common earth), compacted in layers | 39% |
| Clay, compacted in layers | 59% |
| Dumped and shaped, not compacted (it still settles) | at least 15% |
The compacted figures come from the loose and compacted volume factors in the U.S. Army, FM 5-434 Earthmoving Operations (2000), Table 1-1; the settlement allowance for dumped fill from the USDA NRCS, Conservation Practice Standard Dike (Code 356), North Dakota (2003). The fill dirt calculator starts at 25%, between the two cases, and offers 15%, 17%, 25%, 39%, 59%.
Worked examples
A raised bed
A 12 × 4 ft raised bed filled 10 inches deep: 12 × 4 × (10 ÷ 12) = 40 cubic feet, and 40 ÷ 27 = 1.48 cubic yards. With 10% extra for settling that is 1.63, so order 2 cubic yards.
Top-dressing a round lawn
A round lawn 20 ft across, top-dressed 1 inch deep: the area is 3.1416 × (20 ÷ 2)² = 314 square feet, and 314 × 1 ÷ 324 = 0.97 cubic yards, so 1 cubic yard covers it.
Filling a low spot
A 10 × 10 ft low spot averaging 1 ft deep, filled with loam and compacted in layers: 10 × 10 × 1 ÷ 27 = 3.70 cubic yards of space. With the 39% allowance for loam, 3.70 × 1.39 = 5.15, so order 5.5 cubic yards of loose fill. At the calculator's 25% starting allowance it would be 4.63: use the figure that matches your soil and how you will compact it.
Round up, and order by the cubic yard
Round up rather than down. Ordered material can't be returned, but running short means a second order and a second delivery. The order button on the calculators rounds your result up to the next half yard.
Bulk dirt is delivered loose and sold by the cubic yard, which is a volume, so the measurement above is all you need. A yard's weight changes with the soil and how wet it is, but its volume does not. For scale, a cubic yard is 27 cubic feet: 13½ bags of 2 cubic feet.
Ready to order? Fill dirt and topsoil and garden soil are priced for your address, and how bulk delivery works explains scheduling and drop-off.