The bagged material guide
How much does a one-yard super sack cover?
Plan gravel, soil and mulch bags by cubic-yard coverage, depth and project area.
One cubic yard equals 27 cubic feet. Spread evenly, it covers 324 square feet at 1 inch, 162 at 2 inches, 108 at 3 inches or 81 at 4 inches deep.
Measure length and width in feet and depth in inches. Multiply length by width by depth, then divide by 324 to find cubic yards. Round up to whole bags only after calculating the full volume.
These are geometric quantities before settling, compaction and waste. Material type and site preparation can change your requirement. Confirm the depth appropriate for your project rather than assuming every landscape needs 3 inches.