Compost Calculator
Compost by the Yard, Not by the Shovelful
Compost is typically sold by the cubic yard (bulk delivery) or in bags measured in cubic feet, while gardeners think in square feet of bed and inches of depth. Converting between the two by eye tends to run short mid-project or leave a costly surplus. This calculator takes the area you're topdressing and your target depth and returns the volume in both units.
The Formula
Cubic Yards = (Area × Depth in inches) ÷ 324
Dividing by 12 converts the depth from inches to feet within the area calculation; dividing by 324 (12 × 27) goes straight from square-foot-inches to cubic yards in one step.
Worked Example
Topdressing a 150 sq ft vegetable bed with 2 inches of compost:
| Quantity | Value |
|---|---|
| Cubic feet | 25.0 cu ft |
| Cubic yards | 0.926 cu yd |
Choosing a Depth
- Topdressing established beds — a thin 1–2 inch layer worked into the top few inches of soil, typically done once or twice a season.
- New bed preparation — 3–4 inches tilled into native soil to build organic matter before the first planting.
- Mulching around plants — a 1-inch compost layer can double as a light mulch, though bark or wood mulch generally holds moisture better over a full season.
How to Use This Calculator
- Enter the area to be covered in square feet.
- Enter the desired compost depth in inches.
- Select Calculate to get the required volume in both cubic feet and cubic yards.
Related Calculations
For a full raised bed fill rather than a topdressing, see the Raised Bed Soil Calculator, or compare against surface mulch needs with the Mulch Depth Calculator.