Compost Calculator
Work out how much finished compost a garden, lawn or bed needs at any depth — cubic yards for delivery and bags for small areas.
How much compost, by depth
Compost is ordered like a mulch — an area at a depth — but the depths are smaller and the purpose differs: 1–2 in worked into a garden bed feeds the soil for a season, while a lawn takes just a 1/4 in topdressing. The calculator turns your area and depth into the finished compost to buy, in bulk yards and in the 1 and 1.5 cu ft bags garden centers sell.
Volume = area × depth · Yards = cubic feet ÷ 27 · Bags = volume (with waste) ÷ bag size
Example: a 20 × 10 ft bed at 2 in deep needs 33.3 cu ft of compost — with the allowance, 36.7 cu ft: 1.36 cubic yards in bulk, or 37 bags of 1 cu ft.
Making your own? A compost pile is built by volume in roughly a 1:3 mix of greens to browns — one part nitrogen-rich greens (kitchen scraps, fresh clippings) to about three parts carbon-rich browns (dry leaves, straw, shredded paper). A pile smaller than about a cubic yard rarely holds cooking heat, and finished compost comes out at roughly half the volume of what went in — the pile is a reducer, not a copier.
Frequently asked questions
How thick should compost go on a garden bed?
1–2 in worked into the top few inches of soil once a year is the standard feeding for vegetable beds. Trees and shrubs take a 2–3 in surface layer kept off the trunk, and lawns take a thin 1/4 in topdressing, brushed in so the grass blades stand through it.
Can you use too much compost?
Yes — compost is rich, and beds amended heavily year after year can build up phosphorus beyond what plants use. A soil test every couple of years keeps the habit honest; most gardens do well on an inch a year rather than a deep annual blanket.
How much finished compost does a pile make?
Roughly half the starting volume, and often less — a full cubic-yard pile of mixed material may finish at a third to a half of a yard. The calculator counts finished compost, so if you are planning to make your own, double the target and start early.
Is bagged compost the same as bulk?
The material is similar; the price per cubic foot is not — bags commonly cost several times bulk. Bags suit a single bed or a topdressing; past about a yard, a bulk delivery is the economical route, and the calculator shows both counts so you can compare.
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