Compost Calculator
Cubic yards or bags of compost for top-dressing lawns, amending beds and filling raised beds.
This compost calculator converts an area and depth into the cubic yards or bags of compost you need — for top-dressing a lawn, amending garden beds, or as part of a raised-bed soil mix.
Bagged compost is usually 1 or 1.5 cubic feet per bag. The tool draws the area to scale and adds a small settling allowance.
How much for each job
Lawn top-dressing: a thin 1/4 to 1/2 inch layer raked in, about one cubic yard per 650 to 1,300 square feet. Amending a bed: 2 to 3 inches tilled into the top 6 to 8 inches of soil. Raised beds: compost is usually a quarter to a third of the mix, the rest topsoil and aeration material.
One cubic yard covers about 100 square feet at 3 inches, or 324 square feet at 1 inch.
Bulk vs bagged
Bulk compost from a municipal or landscape-supply yard is a fraction of the bagged price and worth it above roughly 8 to 10 bags. Quality varies, though — ask whether it is screened, how long it has cured, and what the feedstock was. Immature compost can rob nitrogen from the soil as it finishes breaking down.
Weight and ordering
Compost is light and mostly organic — about 0.5 to 0.6 tons per cubic yard, less than half the weight of topsoil, so it is sold by volume. It settles and continues to break down, so order about 10% extra and expect the level to drop over the first season.
Common compost mistakes
Using immature compost. Compost still breaking down pulls nitrogen from the soil — ask how long it has cured.
Too thick a top-dress. On a lawn, keep it to 1/4–1/2 inch so the grass grows through; a thick layer smothers it.
Compost as the whole bed. It shrinks and compacts — mix it with topsoil at about one part to three for raised beds.
Bags for a big job. Bulk compost is a fraction of the bagged price past ~10 bags.
| Material | lb / ft³ | tons / yd³ | Sold by | Typical use |
|---|---|---|---|---|
| Screened topsoil (dry) | 75–85 | 1.10 | yd³ (some ton) | New lawns, bed top-up, levelling |
| Topsoil (moist) | 95–110 | 1.40 | yd³ | As delivered after rain — weighs more |
| Fill dirt / structural fill | 90–100 | 1.25 | ton or yd³ | Raising grade, backfill, berms |
| Compost | 40–50 | 0.55 | yd³ or bag | Bed amendment, lawn top-dressing |
| Garden / raised-bed mix | 65–80 | 1.00 | yd³ or bag | Filling raised beds (soil + compost blend) |
Every material calculator
Each of these uses the same measured-drawing tool with the right density and bag sizes built in: gravel calculator , mulch calculator , concrete calculator , concrete slab calculator , sand calculator , topsoil calculator , paver sand calculator , crushed stone calculator , sonotube concrete calculator , pea gravel calculator , river rock calculator , decomposed granite calculator . Or start from the material calculator homepage and pick a material there.
Frequently asked questions
How much compost do I need?
For a bed, 2 to 3 inches worked in — about one cubic yard per 100 to 160 square feet. For lawn top-dressing, a 1/4 to 1/2 inch layer, roughly one cubic yard per 650 to 1,300 square feet.
How many bags of compost are in a cubic yard?
About 27 bags of 1 cubic foot, or 18 bags of 1.5 cubic feet.
How much compost to top-dress a lawn?
A thin 1/4 to 1/2 inch layer raked into the grass. A 1,000 square foot lawn needs about 0.75 to 1.5 cubic yards.
How much does a cubic yard of compost weigh?
About 0.5 to 0.6 tons (1,000 to 1,200 lb) — much lighter than topsoil, which is why it is sold by volume.
How much compost for a 4x8 raised bed?
If compost is a third of the mix in a 12-inch-deep 4 ft × 8 ft bed (32 cubic feet total), that is about 11 cubic feet — roughly 8 to 11 bags.
Is bulk compost better than bagged?
It is much cheaper per yard above about 8 to 10 bags, but quality varies. Ask if it is screened, cured, and what it was made from.
How deep should compost be when amending soil?
Spread 2 to 3 inches and till it into the top 6 to 8 inches, so the finished bed is roughly a quarter compost by volume.
How much extra compost should I order?
About 10%. Compost settles and keeps decomposing, so the level noticeably drops over the first few weeks.
How much compost do I need to top-dress a 5,000 square foot lawn?
At 3/8 inch, about 5.8 cubic yards. At 1/4 inch, about 3.9 cubic yards.
How many bags of compost make a cubic yard?
About 18 bags of 1.5 cubic feet, or 27 bags of 1 cubic foot.
Can you put too much compost in a garden?
Yes — more than about 25–30% compost by volume can hold too much water and over-supply nutrients. Blend it with topsoil rather than planting into pure compost.
How much does a cubic yard of compost weigh?
About 1,000 to 1,200 lb — roughly half the weight of topsoil, which is why it is sold by volume.
When is the best time to top-dress with compost?
Early autumn or spring, right after aerating, so the compost works into the core holes and the grass is actively growing.