Compost Calculator

How it’s calculated

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.

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.

Sources

• Volume = area × (depth ÷ 12) ÷ 27 (geometry); bags = volume ÷ bag size, rounded up. Bag size is product-specific (from the bag).