Material takeoff
How much compost do I need?
Set your area and depth for lawn topdressing or bed amendment. Thin layers are the norm here — a quarter inch goes a long way.
How the math works
cubic yards = square feet × depth in inches ÷ 324
At a quarter inch, one cubic yard topdresses about 1,300 square feet. At half an inch, about 650. Those numbers surprise people who are used to buying mulch — a little compost covers a lot of ground.
How much and how often
Lawn topdressing: a quarter to a half inch, once or twice a year, usually right after core aeration so the material works into the holes. More than half an inch at once risks smothering the turf.
New garden beds: one to two inches worked into the top six to eight inches of soil.
Established beds: half an inch to an inch on the surface annually, letting worms and rain incorporate it.
Under new sod or seed: half an inch to an inch tilled in is a substantial improvement over bare subsoil, and cheaper than importing topsoil for the same effect.
Where people get it wrong
- Applying it like mulch
- Three inches of compost on a lawn kills it. Quarter to half an inch is the topdressing range.
- Using unfinished compost
- Compost that is still actively decomposing pulls nitrogen out of the soil and can burn plants. It should smell like soil, not like a compost pile.
- Composting instead of testing
- Compost fixes organic matter and structure. It does not fix a pH problem. A soil test tells you which one you have.
- Buying bagged for a lawn-sized job
- Topdressing 5,000 square feet at a quarter inch is about 4 cubic yards, which is 72 bags. Bulk is the obvious answer.
Background
Compost is applied far more thinly than mulch, and the depth field is where people go wrong. Lawn topdressing is a quarter to a half inch. Bed amendment is one to two inches worked in. Three inches of compost on a lawn smothers it.
What you need for the job
Common questions
How much compost do I need to topdress a lawn?
A quarter to a half inch. For 5,000 square feet at a quarter inch that is about 3.9 cubic yards.
How much does a yard of compost cover?
At a quarter inch deep, about 1,300 square feet. At one inch, about 324 square feet.
Can I use compost instead of topsoil?
For amending, yes — it is generally better. For filling volume, no. Compost continues to decompose and lose volume, so a bed filled entirely with compost sinks noticeably over a season. Use topsoil for the bulk and mix compost in.
When should I topdress with compost?
Right after core aeration, in early fall for cool-season grass or late spring for warm-season grass.
How much does a yard of compost weigh?
Roughly 1,000 to 1,400 pounds, considerably lighter than topsoil.
Measuring by hand is where estimates go wrong
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