Compost & Mulch Calculator

Find the cubic yards of compost, mulch, or topsoil needed to cover a bed to a chosen depth, plus how many 2 cubic-foot bags that is.

How it works

Volume is the bed area multiplied by the depth. Because depth is entered in inches, it is divided by 12 to convert to feet, and the cubic-foot result is divided by 27 to give cubic yards (the unit bulk material is usually sold in):

Cubic yards = ( length ft × width ft × (depth in ÷ 12) ) ÷ 27

Bagged material is often sold in 2 cubic-foot bags, so the tool also divides the total cubic feet by 2. Order a little extra to allow for settling and uneven ground.

Choosing a depth

Depth depends on the job. A thin topdressing of finished compost is often half an inch to an inch, a mulch layer to suppress weeds and hold moisture is commonly two to four inches, and filling a new raised bed can call for six inches or more. Keep mulch pulled back from plant stems and tree trunks to avoid rot, and let coarse woody mulches age before mixing them into the soil.

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This tool is a planning aid and does the math from the numbers you enter. It is not a substitute for a soil test, seed-tag information, or advice from your local Cooperative Extension office. Page updated Aug 4, 2026.