Bulk materials
Compost Calculator
Compost gets applied far thinner than mulch or soil, and the right depth depends entirely on the job. Enter your area and pick the application to get volume, bags, and cost.
Updated
Area to cover
Add a section for each part of the space. Odd shapes are easiest as two or three simple ones.
Area = length × width
Material and depth
Finished compost smells like forest floor. Sour or ammonia smell means it is not done.
¼–½ in to topdress a lawn, 1–2 in as surface mulch, 2–3 in tilled into a new bed.
5% covers settling and uneven ground. Use 10% on rough or sloped sites.
Only affects the weight figures, never the volume. Typical range 800–1600 lb/cu yd, wet material sits at the top.
Enter your measurements to see results.
How this is calculated
Depth is the whole decision
The volume math is trivial, area times depth. What matters is that compost application depths run from a quarter inch to three inches depending on what you are doing, a twelve-fold range.
Topdressing a lawn uses a quarter to a half inch. Any more and you bury the crowns of the grass. Amending a new bed uses two to three inches tilled into the top six to eight inches of soil. Mulching with compost around established plants uses one to two inches on the surface.
cubic yards = (area sq ft × depth in ÷ 12) ÷ 27
| Application | Depth | Coverage per cu yd |
|---|---|---|
| Lawn topdressing | ¼ in | 1,296 sq ft |
| Heavy lawn topdressing | ½ in | 648 sq ft |
| Surface mulch around plants | 1–2 in | 162–324 sq ft |
| Amending a new bed (tilled in) | 2–3 in | 108–162 sq ft |
| Building raised bed mix | ~30% of fill | See raised bed calculator |
Why a quarter inch is not too little
A quarter inch across 1,000 sq ft is about 0.77 cubic yards, roughly 1,600 lb of material. It looks like almost nothing spread out, and it is still a serious amount of organic matter to add to a lawn in one pass.
Compost topdressing works cumulatively. A quarter inch every autumn does far more for soil structure over five years than two inches once, and it never smothers the turf you are trying to help.
Worked example
Topdressing a lawn after aeration
Spreading a quarter inch of compost over 4,000 sq ft of lawn following core aeration.
- Area
- 4,000 sq ft
- Depth in feet
- 0.25 in ÷ 12 = 0.0208 ft
- Volume
- 4,000 × 0.0208 = 83 cu ft
- Cubic yards
- 83 ÷ 27 = 3.1 cu yd
- Weight
- 3.1 × 1,100 lb ≈ 3,400 lb
About 3 cubic yards. Spread it right after aeration so it works down into the core holes, that is what gets organic matter into the root zone rather than leaving it on the surface.
Frequently asked questions
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