Volume comes first
For a rectangular layer, volume = inside length × inside width × added depth. For a circular layer, volume = π × (inside diameter ÷ 2)² × added depth. Multiply by the number of identical beds.
In feet and inches, convert the depth to feet by dividing inches by 12. In meters and centimeters, divide depth by 100. Top-up depth = target total depth − existing depth; a negative top-up is invalid. If the two are equal, no material is needed.
Our conversion factors
| From | To |
|---|---|
| 1 cubic yard | 27 cubic feet |
| 1 cubic foot | 0.028316846592 cubic meters |
| 1 cubic meter | 1,000 liters |
| 1 foot | 0.3048 meters |
| 1 inch | 2.54 centimeters |
These follow the international foot and inch definitions. See the NIST guide to SI units. Displays are rounded for readability; calculations use the underlying precision.
Allowance and purchase rounding
Order volume = measured volume × (1 + allowance ÷ 100). Allowance defaults to zero. It is your optional input, not a measured settling rate.
Bags = order volume ÷ package volume, rounded up to a whole bag. A small numerical tolerance prevents floating-point noise from turning an exact 15-bag result into 16.
Bulk order = the larger of required cubic yards and the supplier minimum, rounded up to the supplier’s ordering increment. No material needed means no order or delivery charge. Bag cost = bags × price per bag. Bulk cost = ordered yards × price per yard + delivery. All comparison prices are in USD; taxes and bag delivery are excluded unless you include them in your entered quote.
Checked examples
- 8 × 4 ft × 12 in = 32 cu ft = 1.185185… cu yd. At 1.5 cu ft per bag: 22 whole bags.
- 2 × 1 m × 30 cm = 0.6 m³ = 600 L. At 40 L per bag: 15 bags.
- A 4-ft diameter circular bed, 12 inches deep: 4π cu ft, or about 12.57 cu ft.
How project totals work
Soil, mulch and compost are grouped separately. Matching package sizes can be pooled before rounding, but only if you are buying the same product. Different package sizes are shown as mixed, with quantities retained per item. Rounded bags may contain more material than the measured bed volume.
What the tools cannot predict
Irregular ground, moisture, compaction, actual product settling, weight, nutrient needs, supplier quality or delivery feasibility. Rectangles and circles approximate the shape you enter. No vehicle load, structural or plant-health advice is provided.
Formula review: October 15, 2026. Automated checks cover geometry, conversions, invalid input, purchase rounding and material grouping. Report a calculation issue.