Estimate how many cubic yards of compost you need. Each dimension has its own unit selector (in/ft/yd/m).
Compost is sold by the cubic yard. Find each area's volume (length x width x depth), divide by 27 for cubic yards. A 1-2 inch topdressing suits most beds; one cubic yard covers about 160 sq ft at 2 inches. Use the unit selector and add a little for settling.