Methods, Sources & Assumptions
For each bed, volume = area × max(target depth − existing depth, 0). Rectangle area is length × width; circle area is π × diameter² ÷ 4; ring area is π × (outer diameter² − inner diameter²) ÷ 4. Convert inches to feet by dividing by 12, or centimeters to meters by dividing by 100.
Add bed volumes and apply the chosen allowance. A cubic yard contains exactly 27 cubic feet. Bags = volume ÷ bag capacity, rounded up. Bulk ordering rounds up to the chosen increment. Quoted costs use whole bags or the rounded bulk order plus the entered delivery charge; tax and unentered fees are excluded.
Worked check: 20 × 12 ft at 3 in added depth is 60 ft³. A 10% allowance makes 66 ft³, or 2.4444 yd³. That requires 33 two-cubic-foot bags, or a 2.5-yd³ bulk order at half-yard increments.
What the result means
Results are planning estimates. Unrounded values are used in the calculations; rounding is applied for display and whole purchasing units. Changing the unit system resets example values rather than silently treating old numbers as different units. The calculator rejects invalid dimensions and impossible combinations.
Sources
- How to Determine the Amount of Mulch Needed for a Garden Bed
- Mulching for soil and garden health
- Choosing and Installing Mulches
- Mulches for Home Gardens
- NIST Guide to SI, Appendix B.8 — Conversion factors
Corrections
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