Estimate how many cubic yards of fill dirt you need. Each dimension has its own unit selector (in/ft/yd/m).
Fill dirt is sold by the cubic yard. Measure each area's volume (length x width x average fill depth), divide by 27 for cubic yards, then add 10-20% for compaction. Fill dirt is cheaper than topsoil - use it for structure and reserve topsoil for the planting layer. Switch units on any field.