How the Compost Calculator Works
Compost follows the same volume math as mulch and topsoil — length × width × depth — but the right depth differs sharply by job, which is where most people overbuy or underbuy. Bed preparation wants 1–2 inches worked into the soil; a brand-new or exhausted bed can take 3 inches; and lawn topdressing needs only a quarter to half inch, because any more smothers the grass instead of feeding it. The preset menu fills in these depths for you. Weight is estimated at 0.65 tons per cubic yard — compost is roughly half the weight of topsoil.
Worked Example: Topdressing a Lawn
Topdressing a 50 × 40 ft lawn (2,000 sq ft) at a half inch: 2,000 × 0.5/12 = 83.3 cubic feet = 3.09 cubic yards — about 2 tons, or a single small dump delivery. In bags it would be 84 one-cu-ft bags, so bulk is the only sensible option for lawns. For a 25 × 10 ft vegetable bed refreshed with 2 inches, you'd need 41.7 cu ft = 1.54 yards, right at the threshold where bulk delivery starts beating bagged.
Blending Compost Into Raised Beds
Filling raised beds? A well-tested mix is 60% topsoil, 30% compost, 10% aeration (perlite or coarse bark). Compute the bed's total volume here or in the topsoil calculator, then take 30% of that figure as your compost order. After planting, finish with 2 inches of mulch from the mulch calculator to lock in moisture — the coverage chart has per-bag numbers for small beds.