How to use this calculator
- Choose your project. Each one uses a recommended depth; choose “Custom depth” to set your own.
- Add the area you want to cover, as one or more rectangles, circles or a known square footage.
- Pick a bag size and, optionally, enter bag and bulk prices to compare costs.
Recommended compost depths
| Project | Depth | Cubic yards per 1,000 sq ft |
|---|---|---|
| New garden or landscape bed (mixed in) | 3–4 in | 9.3–12.3 |
| Established vegetable bed (yearly top-up) | ¼–1 in | 0.8–3.1 |
| New lawn (mixed in before seeding or sod) | 1–2 in | 3.1–6.2 |
| Existing lawn (topdressing) | ¼–½ in | 0.8–1.5 |
These depths come from Oregon State University Extension’s guide to using compost. The calculator uses 3 inches for new beds, 1 inch for top-ups, 2 inches for new lawns and ¼ inch for topdressing, all of which you can change.
The formula
- Cubic feet = area (sq ft) × depth (in) ÷ 12
- Cubic yards = cubic feet ÷ 27
- Bags = cubic feet ÷ bag size, rounded up
Worked examples
New vegetable garden. A 20 × 10 foot plot with 3 inches of compost mixed in: 200 × 3 ÷ 12 = 50 cubic feet, about 1.85 cubic yards. That is 50 bags of 1 cubic foot, so this is a job where bulk compost usually saves money.
Lawn topdressing. A 4,000 square foot lawn with ¼ inch of compost: 4,000 × 0.25 ÷ 12 ≈ 83 cubic feet, about 3.1 cubic yards.
Tips for using compost
- Mix it in for new beds. Spread the compost, then dig or till it into the top 6 to 8 inches of soil so roots grow into improved soil, not just a layer on top.
- Use mature compost. Finished compost is dark, crumbly and smells earthy. Raw or hot compost can tie up nitrogen and harm young plants.
- Don’t overdo it every year. Once beds are established, a thin yearly layer is plenty. Very heavy yearly applications can build up more nutrients, such as phosphorus, than plants need.
Sources
Frequently asked questions
How much compost should I add to my garden?
Oregon State University Extension suggests about 3 to 4 inches mixed into the soil when starting new garden or landscape beds, and about ¼ to 1 inch a year as a top-up for established vegetable beds.
How much compost do I need per 1,000 square feet?
One inch of compost over 1,000 square feet is about 83 cubic feet, or roughly 3.1 cubic yards. Multiply that by the depth in inches you plan to apply.
How much compost for a new lawn?
Oregon State University Extension suggests mixing 1 to 2 inches of compost into the soil before seeding or laying sod, which is about 3.1 to 6.2 cubic yards per 1,000 square feet.
Can I topdress my lawn with compost?
Yes. A thin layer of about ¼ to ½ inch, raked into the grass so the blades still show, improves the soil over time. It works especially well right after core aeration.
How many bags of compost are in a cubic yard?
A cubic yard is 27 cubic feet: 27 bags of 1 cubic foot, 18 bags of 1.5 cubic feet, or 36 bags of 0.75 cubic feet.