Data Source and Methodology
- USDA NRCS — Soil Quality Information Sheet: Soil Bulk Density (Updated). United States Department of Agriculture, Natural Resources Conservation Service. 1999, updated 2011. Direct link: nrcs.usda.gov Soil Bulk Density PDF.
- NIST Special Publication 811 — Guide for the Use of the International System of Units (SI). National Institute of Standards and Technology. 2008 (updated 2019). Reference conversions used for ft–m and L–ft³. nist.gov/sp-811.
Tutti i calcoli si basano rigorosamente sulle formule e sui dati forniti da questa fonte.
The Formula Explained
Area by shape:
Rectangle: \( A_{\mathrm{rect}} = L \times W \)
Circle: \( A_{\mathrm{circ}} = \pi \left(\frac{D}{2}\right)^2 \)
Triangle: \( A_{\mathrm{tri}} = \frac{1}{2} \times B \times H \)
Depth conversion:
Imperial: \( d_{\mathrm{ft}} = \frac{d_{\mathrm{in}}}{12} \quad\quad \) Metric: \( d_{\mathrm{m}} = \frac{d_{\mathrm{cm}}}{100} \)
Volume:
Imperial: \( V_{\mathrm{ft}^3} = A_{\mathrm{ft}^2} \times d_{\mathrm{ft}} \), then \( V_{\mathrm{yd}^3} = \frac{V_{\mathrm{ft}^3}}{27} \)
Metric: \( V_{\mathrm{m}^3} = A_{\mathrm{m}^2} \times d_{\mathrm{m}} \), then \( V_{\mathrm{yd}^3} = \frac{V_{\mathrm{m}^3}}{0.764554858} \)
Weight estimate (short tons): \( W_{\mathrm{tons}} = \rho_{\mathrm{t/yd^3}} \times V_{\mathrm{yd}^3} \)
Bag count (rounded up): \( n_{\mathrm{bags}} = \left\lceil \frac{V_{\mathrm{ft}^3}}{V_{\mathrm{bag}}} \right\rceil \)
Glossary of Variables
- L, W — Length and Width (ft or m)
- D — Diameter (ft or m)
- B, H — Base and Height of triangle (ft or m)
- d — Depth (in or cm; internally converted to ft or m)
- A — Area (ft² or m²)
- V — Volume (ft³, yd³, or m³)
- ρ (rho) — Density in short tons per cubic yard (t/yd³)
- n_bags — Number of bags required
- V_bag — Bag volume (ft³)
How It Works: A Step-by-Step Example
Scenario: Two rectangular beds with a uniform depth of 6 inches (imperial), moist topsoil density 1.1 t/yd³. Bed A: 20 ft × 10 ft. Bed B: 12 ft × 8 ft.
- Areas:
- Bed A area: \( A_1 = 20 \times 10 = 200 \,\mathrm{ft}^2 \)
- Bed B area: \( A_2 = 12 \times 8 = 96 \,\mathrm{ft}^2 \)
- Total area: \( A = 296 \,\mathrm{ft}^2 \)
- Depth: \( d_{\mathrm{ft}} = \frac{6}{12} = 0.5 \,\mathrm{ft} \)
- Volume: \( V_{\mathrm{ft}^3} = 296 \times 0.5 = 148 \,\mathrm{ft}^3 \)
- Convert to cubic yards: \( V_{\mathrm{yd}^3} = \frac{148}{27} \approx 5.48 \,\mathrm{yd}^3 \)
- Weight: \( W = 1.1 \times 5.48 \approx 6.03 \) short tons
- If using 2.0 cu ft bags: \( n = \lceil 148 / 2.0 \rceil = \lceil 74 \rceil = 74 \) bags
Frequently Asked Questions (FAQ)
What depth should I use for new lawns and garden beds?
New lawns commonly use 3–6 inches (7.5–15 cm). Vegetable beds often use 8–12 inches (20–30 cm). Increase depth for poor native soil.
What’s the difference between bulk and bagged topsoil?
Bulk topsoil is delivered by the cubic yard and is cost-effective for larger projects. Bagged topsoil is convenient for small projects and transport by car.
Does the calculator account for slope?
No. The calculator assumes uniform depth. For sloped areas, estimate an average depth or split the area into multiple sections with different depths.
How do moisture and organic matter affect weight?
Moisture increases density; organic matter can decrease it. Use presets as a guide and choose “Custom” if you have a supplier-provided density.
Can I mix metric and imperial inputs?
Select one unit system per calculation. Change the unit system to switch between metric and imperial; values and labels update accordingly.
Is the result suitable for ordering?
Yes, but consider adding a 5–10% contingency for settling, spillage, and site variability, especially for hand-graded installations.