Data Source and Methodology
Authoritative Data Source: Wolfram MathWorld — Geometric Area Formulas (accessed 2025), and NIST Special Publication 811 — Guide for the Use of the International System of Units (SI) (2008 Edition). All conversions and geometric calculations follow these references.
- Wolfram MathWorld. “Area.” https://mathworld.wolfram.com/Area.html
- NIST SP 811. “Guide for the Use of the International System of Units (SI).” https://www.nist.gov/pml/special-publication-811
Tutti i calcoli si basano rigorosamente sulle formule e sui dati forniti da questa fonte.
The Formula Explained
Area and volume are computed using the selected shape and depth:
Rectangle: $$A = L \times W$$
Circle: $$A = \pi \left(\frac{d}{2}\right)^2$$
Triangle: $$A = \frac{1}{2} \times b \times h$$
Ring/Annulus: $$A = \pi \left(R^2 - r^2\right)$$
Known area: $$A = A_{given}$$
Depth normalization: $$d_{ft} = \frac{d_{in}}{12} \quad;\quad d_{m} = \frac{d_{cm}}{100}$$
Volume: $$V = A \times d$$
Unit conversions: $$V_{yd^3}=\frac{V_{ft^3}}{27} \quad;\quad V_{m^3} = V_{ft^3}\times 0.028316846592 \quad;\quad V_L = V_{m^3}\times 1000$$
Bag count: $$\text{Bags} = \left\lceil \frac{V_{ft^3}}{\text{Bag}_{ft^3}} \right\rceil$$
Coverage per bag: $$\text{Coverage} = \frac{\text{Bag}_{ft^3}}{d_{ft}}$$
Glossary of Variables
- L, W — Length and width of a rectangle (ft or m).
- d — Circle diameter (ft or m).
- b, h — Triangle base and height (ft or m).
- R, r — Outer and inner radius of ring (ft or m).
- Depth — Mulch thickness (in or cm); normalized to feet/meters for volume.
- A — Area (sq ft or m²).
- V — Volume (cu ft, cu yd, m³, or liters).
- Bag size — Volume per bag (cu ft or liters).
- Bags — Number of bags needed (rounded up).
- Coverage per bag — Area one bag covers at the chosen depth.
- Costs — Optional estimates using price per bag or per cubic yard.
How It Works: A Step-by-Step Example
Scenario: A 20 ft × 10 ft rectangular bed with 3 inches of mulch, using 2 cu ft bags.
- Area: A = 20 × 10 = 200 sq ft.
- Depth in feet: d_ft = 3 ÷ 12 = 0.25 ft.
- Volume: V = 200 × 0.25 = 50 cu ft.
- Cubic yards: 50 ÷ 27 ≈ 1.852 cu yd.
- Bags: 50 ÷ 2 = 25 bags (round up if needed).
- Coverage per bag at 3 in: Coverage = 2 ÷ 0.25 = 8 sq ft/bag.
This matches the calculator’s outputs when the same inputs are provided.
Frequently Asked Questions (FAQ)
What depth should I use?
Most beds perform best at 2–3 inches (5–7.5 cm). Avoid piling mulch against trunks or stems.
Is it better to buy bags or bulk?
For small projects, bags are convenient. For larger areas, bulk by the cubic yard is often more economical. Compare both using cost fields.
Why do I need to round up bags?
Material settles and coverage varies around edges. Rounding up prevents shortages and uneven coverage.
Does mulch moisture change the volume?
No. Moisture affects weight, not geometric volume. This tool calculates volume; delivery limits may be weight-based.
Can I mix shapes and multiple beds?
Yes. Enable “multiple areas” to add different shapes and sum them automatically.
How accurate are the unit conversions?
Conversions use NIST SP 811 factors. 1 cu ft = 28.316846592 L; 1 cu yd = 27 cu ft.
Do I need to include landscape fabric thickness?
No. Fabric does not significantly affect mulch volume; only the area and mulch depth matter.