Soil Calculator
Volume = length × width × depth (or πr² × depth)
How Garden Soil Volume Calculations Work
Garden soil volume follows the same math as concrete and mulch: volume (cu ft) = area × depth in feet. A rectangular 12 ft × 4 ft raised bed filled 12 inches (1 ft) deep needs 12 × 4 × 1 = 48 cubic feet. Convert to cubic yards: 48 ÷ 27 = 1.78 yd³. Bagged topsoil often comes in 1.5 cu ft bags: 48 ÷ 1.5 = 32 bags.
Circular beds use π × radius² × depth. A 6 ft diameter round planter (3 ft radius) 10 inches deep: depth = 10/12 = 0.833 ft. Volume = π × 3² × 0.833 = 23.6 cu ft, or 0.87 yd³ — about 16 bags. Raised beds typically need 10–18 inches of quality topsoil mix over drainage gravel. In-ground beds benefit from 4–6 inches tilled into native soil.
Soil mix ratios for raised beds often blend topsoil, compost, and perlite or sand. A 50/30/20 mix improves drainage and fertility over straight topsoil. Soil compacts 10–20% after watering and settling — fill slightly proud of the bed edge. For lawn establishment, calculate coverage in cubic yards and spread evenly before seeding or sodding.
Weight limits matter for balconies and rooftop gardens — saturated soil weighs roughly 100 lb per cubic foot. A 48 cu ft bed holds nearly 2.4 tons wet. Compare with the gravel-mulch calculator for mulch and decorative stone in adjacent landscape beds.
| Bed Size | Depth | Volume | Bags (1.5 cu ft) |
|---|---|---|---|
| 12×4 ft rectangular | 12 in | 48 cu ft (1.78 yd³) | 32 |
| 12×12 ft garden | 6 in | 72 cu ft (2.67 yd³) | 48 |
| 6 ft diameter round | 10 in | 23.6 cu ft | 16 |
| 8×3 ft raised bed | 18 in | 36 cu ft (1.33 yd³) | 24 |
Choose rectangular or circular bed shape, enter dimensions and depth, and get cubic feet, cubic yards, and bag counts. Use the square footage calculator to measure irregular beds split into rectangles.
Examples
| Example | Result |
|---|---|
| 12×4 ft raised bed, 12 in deep | 48 cu ft, 1.78 yd³, 32 bags |
| 12×12 ft garden, 6 in topsoil | 72 cu ft, 2.67 yd³ |
| 6 ft round planter, 10 in deep | 23.6 cu ft, 16 bags |
| 8×3 ft bed, 18 in deep | 36 cu ft, 24 bags |
| 10×10 ft plot, 8 in soil | 66.7 cu ft, 2.47 yd³ |
| 4 ft round herb garden, 12 in | 12.6 cu ft, 9 bags |
| 16×4 ft vegetable row, 10 in | 53.3 cu ft, 36 bags |
Frequently asked questions
Raised beds need 10–18 inches of quality soil. In-ground vegetable gardens benefit from 6–12 inches of amended topsoil tilled into the native earth.
One cubic yard is 27 cubic feet. At 1.5 cu ft per bag, that is 18 bags per cubic yard. Bulk delivery is cheaper above 2–3 cubic yards.
Yes. Enter the planter dimensions as a rectangular or circular bed. Shallow containers under 6 inches deep use the depth in inches directly.