How Deep and How Much Mulch?
Mulch is usually spread 2-4 inches deep. Beds and tree rings take 2-3 inches, while weedy or sloped areas need 3-4 inches; too deep can smother roots. Volume in cubic yards equals area in square feet times depth in inches divided by 324. Bags are often 2 cubic feet, and about 27 bags make one cubic yard.
Depth
Beds and vegetable gardens: 2-3 inches; tree rings: 2-3 inches, kept away from the trunk.
Slopes or heavy weeds: 3-4 inches, but do not exceed 4 inches.
Top up 1-2 inches a year instead of replacing all mulch.
How much to buy
Measure the area, then use the volume formula; add 5-10% for safety.
Bulk is sold by cubic yard and bags by cubic foot; check the label.
FAQ
Can I mulch over old mulch?
Yes, rake and break up matted layers first; keep total depth under 4 inches.
How much does a 2 cubic foot bag cover?
About 12 square feet at 2 inches, or 8 square feet at 3 inches.