To find how much mulch you need, multiply the bed's area in square feet by the depth in inches and divide by 324. The result is cubic yards; multiply by 27 to get cubic feet for bagged mulch. University of Illinois Extension recommends a layer of 2–4 inches, kept at least 4 inches away from tree trunks.
Bed dimensions
University of Illinois Extension recommends 2–4 inches of mulch for most beds, kept at least 4 inches away from tree trunks and plant stems.
Mulch depth guide
2 inches: appropriate over perennial beds and around herbaceous plants where the crowns are at ground level. Suppresses most weeds, holds moisture, doesn't risk crown rot.
3 inches: the standard for shrub borders, foundation plantings, and around small trees. Top up annually as the mulch decomposes into the soil.
4+ inches: reserved for paths or unplanted areas where weed suppression is the only goal. Avoid this depth over root zones — it can trap moisture against bark and promote rot.
Volcano mulching is wrong. Mounding mulch against a tree trunk holds moisture against the bark and invites rot and rodents. Keep mulch at least 4 inches away from the trunk (University of Illinois Extension): a donut, not a volcano.
Sources: University of Illinois Extension: Proper Mulching Techniques (Tree Care Basics infosheet, PDF), Clemson Cooperative Extension HGIC: Mulch, Colorado State University Extension: 1609 – Organic Mulches (PlantTalk Colorado).
Frequently asked
How much mulch do I need?
Multiply the area in square feet by the depth in inches, then divide by 324 to get cubic yards. For example, a 200 sq ft bed at 3 inches deep needs 200 × 3 ÷ 324 ≈ 1.85 cubic yards, which is about 50 cubic feet or 25 two-cubic-foot bags.
How many cubic feet are in a yard of mulch?
One cubic yard of mulch is 27 cubic feet (3 ft × 3 ft × 3 ft). Bulk mulch is sold by the cubic yard; bagged mulch is labeled in cubic feet.
How many bags of mulch are in a yard?
It depends on bag size: 13.5 bags of 2 cubic feet, 9 bags of 3 cubic feet, or 18 bags of 1.5 cubic feet make one cubic yard. Round up to whole bags.
How much does one cubic yard of mulch cover?
One cubic yard covers 324 sq ft at 1 inch deep, 162 sq ft at 2 inches, 108 sq ft at 3 inches and 81 sq ft at 4 inches. At 3 inches deep, each square foot takes 0.25 cubic feet of mulch.
How deep should mulch be?
University of Illinois Extension recommends 2–4 inches: 2–3 inches for composted materials and 3–4 inches for coarse mulches. Colorado State University Extension notes organic mulches such as wood chips need to be 3–4 inches thick to keep weeds down. Keep mulch at least 4 inches from tree trunks; Illinois Extension warns that mulch piled against a tree softens the bark, which can lead to insects, diseases and root girdling.