Compost Calculator
Compost is spread in a thin layer to feed the soil. Enter your area and the depth for the cubic yards (bulk) or bags to buy.
Compost
0.62cu yd
- Volume
- 17 cu ft
- Bags
- 12 bags
How these numbers are worked out
The formula
Volume = area × (depth ÷ 12) cubic feet, ÷ 27 for cubic yards. Bags = volume ÷ the bag's cubic feet, rounded up. The depth is what matters: compost is an amendment spread thin, not a bulk fill — much less than topsoil or mulch.
Constants and sources
- Volume = area × (depth ÷ 12) ÷ 27 (geometry); bags = volume ÷ bag size, rounded up. Bag size is product-specific (from the bag).
How it was checked
Last reviewed . Before this calculator was published, its formula, constants and worked example were checked in a separate, AI-assisted review that redid the arithmetic and tested the factual claims; the site owner then approved it for publishing. No engineer or tradesperson reviews these pages. Where a figure depends on the product (a density, a coverage rate, a bag size), it is either an input you can change above or a fixed planning value stated on this page, so check it against your product's label or your supplier.
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Worked example
A 10 × 10 ft bed (100 sq ft) topped with 2 in of compost: 100 × 2 ÷ 12 = 16.7 cu ft = 0.62 cu yd, or ⌈16.7 ÷ 1.5⌉ = 12 bags of 1.5-cu-ft compost.
FAQs
- How deep should I spread compost?
- Thin. To topdress a lawn, about ¼–½ inch raked in. To amend a garden bed, 1–3 inches worked into the top several inches of soil. Topping a brand-new bed can take up to ~3 inches. More isn't better — see below.
- Can I use too much compost?
- Yes. Piling on compost over-loads the soil with nutrients and salts, which can harm plants and run off into waterways, and a thick mat can hold too much moisture. Compost is a soil improver applied in thin layers, not a growing medium you fill a bed with.
- Compost or topsoil?
- Different jobs. Topsoil is bulk mineral soil for filling, leveling, and grading; compost is decomposed organic matter you mix into soil to improve it. For a new bed many gardeners blend the two — use the topsoil calculator for the bulk fill and this for the compost amendment.