How the number is worked out
Area times depth gives cubic feet, divided by 27 gives cubic yards. At half an inch over a lawn the yardage is small and easy to over-order by a factor of four, so type the depth you mean, not the depth that sounds generous.
area (ft²) × depth (ft) ÷ 27 = cubic yards
How much for what
Top-dressing a lawn: a quarter to half an inch, raked in so the grass shows through — a yard covers 650 to 1,300 square feet. Feeding an established bed: an inch on the surface each year, left for the worms. Building a new bed or fixing poor soil: two to three inches turned into the top six, which puts compost at about a quarter to a third of the mix. More than that and beds sink as it breaks down.
Compost, mulch and topsoil
They are sold side by side and do different jobs. Compost feeds soil and is worked in. Mulch sits on top to hold water and stop weeds. Topsoil is soil — bulk, structure, something to plant into. Compost spread three inches thick as a mulch works but is expensive; topsoil used as an amendment adds little. Use the mulch and topsoil calculators for those layers.
What to ask for
Finished, screened and weed-free. Finished compost is dark, crumbly and smells of earth, not ammonia; unfinished compost steals nitrogen from the bed while it keeps breaking down. Screened means sticks and stones are out. Ask what it was made from — leaf and yard compost is the safe option for beds. Manure-based compost can contain more soluble salts. Buy mature compost suited to your plants; waiting a fixed number of months does not establish its maturity or salt level.
Depth by use
| Job | Depth | One yard covers |
|---|
| Lawn top-dressing | ¼ to ½ in | 650 to 1,300 ft² |
| Feeding an established bed | 1 in | about 320 ft² |
| Amending a new bed (tilled in) | 2 to 3 in | 110 to 160 ft² |
| Filling raised beds (25–30% of mix) | by volume | see cubic yards |
Questions
How much does a cubic yard of compost weigh?
The default estimate is 1,000 pounds per cubic yard, but moisture and the source material change the weight. Ask the supplier, then check available vehicle payload after occupants and other cargo; the term half-ton pickup is not a loading limit.
How many bags of compost in a cubic yard?
Twenty-seven of the one-cubic-foot bags, eighteen at 1.5 cubic feet, or about fourteen of the two-cubic-foot bags. Bulk wins on price past about half a yard.
Can I top-dress a lawn with compost?
Yes, and it is the best thing you can do for one. Quarter to half an inch, raked or dragged in so the blades stand clear, ideally after aerating. Thicker than that smothers the grass.
Compost or topsoil for a new bed?
Both. Topsoil gives the bed its bulk; compost, mixed through at a quarter to a third, gives it life. Compost alone sinks as it breaks down, and pure topsoil from a yard is often poor.
Other calculators
The same ticket, the same assumptions on screen, for whatever else the job needs.
Concrete slabs, footings, columns and stepsGravel driveways, bases and drainage stoneRiver rock beds, borders and dry creeks, by stone sizeMulch beds and trees, by the yard or the bagAsphalt hot mix by the tonTopsoil beds, lawns and levellingFill dirt holes, grades and backfill, with settlingSand paver bedding, play sand and fillCubic yards any volume, in every unitRebar bars, sticks, laps and weight