Part of the Agriculture collection — 4 tools available
Compost Calculator
Calculate how much compost you need for garden beds and raised beds. Estimate cubic yards, bags, and cost based on bed dimensions and desired depth.
About This Calculator
Compost is garden gold — it improves soil structure, adds slow-release nutrients, and boosts microbial activity that makes other nutrients more available to plants. But figuring out how much to buy for your garden beds can be confusing, especially when navigating between bulk cubic yard deliveries and retail bags that hold about 1 cubic foot each. Garden centers sell compost in 40-pound bags, while landscape supply yards sell it by the cubic yard. Our compost calculator converts your garden bed dimensions and desired application depth into both units so you can compare prices.
The Formula Behind This Calculator
C:N ratio target = 25-30:1 Volume (cu yd) = L * W * H / 27 Moisture target: 50-60%.
Understanding the math helps you verify results and make better decisions for your project.
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How to Use
- 1Measure your garden bed or area length and width in feet.
- 2Set desired compost depth in inches (1-2" for top-dressing, 3-4" for new beds).
- 3Enter price per 40-lb bag from your garden center.
- 4Click Calculate for cubic yards, bags, and cost.
When to Use
- →Top-dressing garden beds with compost before the growing season starts
- →Filling new raised beds with a compost-soil mix and needing to know how many bags or yards to order
- →Comparing the cost of bulk compost delivery vs buying individual bags at the garden center
Tips
- ✓More than 3 inches of compost at once can create drainage problems and nutrient imbalances — apply in thinner layers
- ✓Bulk delivery is usually cheaper than bags if you need more than 10 bags — check both options before buying
- ✓Apply compost in fall or early spring, 2-4 weeks before planting, so nutrients have time to integrate into the soil
FAQ
How deep should I spread compost on garden beds?
Top-dressing existing beds: 1-2 inches worked into the top few inches of soil. New raised beds: fill with a mix of 30% compost to 70% topsoil.
How many bags of compost equal a cubic yard?
About 27 forty-pound bags equal one cubic yard. If you need more than 10 bags, bulk delivery is usually cheaper.
Can I use too much compost?
Yes. More than 3 inches layered at once can create drainage problems and nutrient imbalances. Excess phosphorus from over-composting is an environmental concern.
When is the best time to add compost?
Fall or early spring. Fall application allows nutrients to integrate over winter. Spring application should be done 2-4 weeks before planting.
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