Compost Calculator
Estimate compost in cubic yards and bags for soil amendment, raised beds, and garden prep.
Your Compost Estimate
- Enter area — length and width of the bed or lawn to amend.
- Set depth — 1" for lawn top-dressing, 2–3" for garden beds, 4–6" for raised bed mix.
- Adjust density — 50 lb/ft³ for standard finished compost. Mushroom compost and manure-based may differ.
- Low waste — 5% — compost doesn't compact or blow away significantly.
- Mix into soil — for garden beds, till compost into the top 6–8 inches of existing soil.
How Much Compost Do I Need?
For existing garden beds, spreading 2 to 3 inches of compost and tilling it into the top 6 inches of soil is the standard recommendation. This adds organic matter, improves drainage in clay soils, and increases water retention in sandy soils. For lawns, a 1/4 to 1/2 inch top-dressing after core aeration helps build soil health over time.
For raised bed fills, a 30–40% compost blend works well — mix with topsoil and a drainage amendment (perlite or coarse sand). Pure compost is too rich and holds too much moisture for most plants. For new garden beds on poor soil, start with 3 inches of compost tilled in, then add 1 inch annually.
Compost Application Rates
Match the depth and method to your goal:
| Application | Depth | Method | Frequency |
|---|---|---|---|
| Lawn top-dressing | ¼–½ in | Spread after aeration, rake in | 1–2× per year |
| Existing garden bed | 2 in | Spread and till into top 6 in | Annually in spring |
| New garden bed | 3 in | Till into top 8 in | Once at establishment |
| Raised bed mix | 4–6 in | Blend with topsoil (30–40%) | Once at setup |
| Tree planting | — | 50/50 compost and native soil | At planting |
Don't over-apply compost — more is not always better. Excessive compost can lead to nutrient imbalances, water-logging, and phosphorus buildup in the soil.
Formulas
Volume calculation:
Cubic yards = Volume ÷ 27
Weight (tons) = Volume × 50 ÷ 2,000
40 lb bags = Weight (lb) ÷ 40
Compost density varies with moisture and material. Dry, screened compost: ~40–50 lb/ft³. Wet, heavy compost: ~60–70 lb/ft³.
Related Calculators
Compost is most effective blended with topsoil. See our full landscaping calculator collection for sod, mulch, and lawn seed.
Frequently Asked Questions
Can I use pure compost as garden soil?
Not recommended. Pure compost is too nutrient-dense, retains too much moisture, and can burn plant roots. Blend compost at 25–40% with topsoil for the best growing medium. The exception is mushroom compost, which is milder and can be used as a thicker layer.
How much does a cubic yard of compost weigh?
Finished compost typically weighs 800–1,200 lbs per cubic yard depending on moisture content. Dry compost is lighter; freshly screened or wetter compost is heavier. A standard pickup truck (half-ton) can safely carry about ½ cubic yard. Always check your truck's payload rating — overloading damages suspension and tires.
How much compost should I add to a garden bed?
For a new garden bed, apply 2–4 inches of compost and till it into the top 6–8 inches of soil. For established beds, a 1–2 inch topdressing each season is enough. More is not always better — excessive compost can raise phosphorus levels and create nutrient imbalances. Use the calculator above to find how many cubic yards you need for your bed dimensions.
What is the difference between compost and mulch?
Compost is decomposed organic material worked into soil to improve structure and fertility — it is a soil amendment. Mulch is applied to the soil surface to retain moisture, suppress weeds, and moderate soil temperature — it is a surface treatment. Some materials like wood chips can serve as mulch on top and eventually break down into compost, but they serve different functions when freshly applied.
Can I use compost alone to level or grade a yard?
Compost is great as a top-dressing and soil amendment, but it's not ideal as a structural leveling material because it decomposes and settles. For grading, use fill dirt or topsoil for the bulk layer, then add compost as a finish layer.