Compost Calculator
The Compost Calculator estimates the total volume of compost required for your project based on area dimensions and desired depth. This calculator is designed to help gardeners, landscapers, and homeowners plan material purchases efficiently. Whether you're preparing a new garden bed, top-dressing a lawn, or amending soil for planting, this tool provides accurate volume estimates for your compost needs.
This calculator is for informational purposes only. Verify results with appropriate professionals for important decisions. Actual compost needs may vary based on soil conditions and application method.
How This Calculator Works
- Enter the length and width of the area you want to cover with compost.
- Specify the desired depth of your compost layer in inches.
- Select your bag size from common retail options (1-3 cubic feet).
- Click Calculate to see the total volume needed and number of bags to purchase.
How Compost Volume Is Calculated
The calculator determines compost volume using the geometric formula for a rectangular prism, treating the coverage area as a three-dimensional space. The area's length and width establish the base, while the depth determines how thick the compost layer will be.
Volume (ft³) = Length (ft) × Width (ft) × [Depth (in) ÷ 12]
Where:
- Length = The longer dimension of your coverage area
- Width = The shorter dimension of your coverage area
- Depth is divided by 12 to convert inches to feet
- Volume (yd³) = Volume (ft³) ÷ 27 (conversion factor)
- Bags Needed = Volume (ft³) ÷ Bag Size (rounded up)
The calculator converts between cubic feet and cubic yards since bulk compost is often sold by the cubic yard, while bagged compost is sold by cubic feet. All calculations round bags up to ensure you have sufficient material for your project.
What Your Compost Volume Means
The estimated volume tells you exactly how much compost to purchase for your project. Understanding typical application depths helps ensure you apply the right amount for your specific gardening goals.
| Application Type | Recommended Depth | Best For |
|---|---|---|
| Top-Dressing Lawn | 0.25 - 0.5 inches | Light lawn renovation and nutrient boost |
| Mulching | 2 - 3 inches | Weed suppression and moisture retention |
| Garden Bed Amendment | 3 - 6 inches | New beds or heavy soil improvement |
| Raised Bed Filling | 6 - 12 inches | Creating new raised garden beds |
Planning Considerations
- For New Gardens: A 4-6 inch layer worked into soil improves structure and fertility for establishing plants.
- For Established Beds: A 1-2 inch top-dressing annually replenishes nutrients without disturbing plant roots.
- For Lawns: Spread a thin 0.25-0.5 inch layer after aeration to improve soil quality without smothering grass.
- For Bulk Purchases: One cubic yard equals 27 cubic feet, typically covering 324 square feet at 1 inch deep.
Consider ordering 5-10% extra to account for settling and uneven ground. Compost continues to decompose over time, so a slightly thicker initial application may maintain coverage longer.
References
- United States Department of Agriculture (USDA) - Natural Resources Conservation Service: Soil Health Management
- University of California Division of Agriculture and Natural Resources - Compost Use Guidelines
- U.S. Composting Council - Landscape Architecture Foundation Guidelines
Calculation logic verified using publicly available standards.
View our Accuracy & Reliability Framework →