Mulch Coverage Calculator
Determines how many cubic yards of mulch to buy for a garden bed or landscape area. Use it before purchasing mulch to avoid under-buying or costly overstock.
About this calculator
Mulch volume is calculated by converting a rectangular area and a depth (in inches) into cubic yards — the standard unit sold by landscaping suppliers. The core formula is: cubic yards = (length × width × (depth ÷ 12)) ÷ 27. Dividing depth by 12 converts inches to feet, and dividing by 27 converts cubic feet to cubic yards. A wastage factor accounts for settling, uneven spreading, and edge overfill: final volume = base volume × (1 + wastage ÷ 100). Most landscapers add 5–10% wastage for typical beds and up to 15% for irregular shapes. Knowing the exact volume prevents multiple supplier trips and helps you compare bulk versus bagged mulch costs.
How to use
Suppose you have a garden bed that is 20 ft long × 8 ft wide, and you want 3 inches of mulch depth with a 10% wastage factor. Step 1 — base volume: (20 × 8 × (3 ÷ 12)) ÷ 27 = (20 × 8 × 0.25) ÷ 27 = 40 ÷ 27 ≈ 1.48 cubic yards. Step 2 — apply wastage: 1.48 × (1 + 10 ÷ 100) = 1.48 × 1.10 ≈ 1.63 cubic yards. Round up to 2 cubic yards when ordering to be safe.
Frequently asked questions
How many cubic yards of mulch do I need for a 100 square foot garden bed?
At the standard recommended depth of 3 inches, a 100 sq ft bed requires (100 × 0.25) ÷ 27 ≈ 0.93 cubic yards, so you would typically order 1 cubic yard. At 2 inches deep the requirement drops to about 0.62 cubic yards. Always add a 5–10% wastage buffer to account for settling and irregular edges. One cubic yard of mulch covers roughly 100–160 sq ft depending on depth.
What is the recommended mulch depth for flower beds and trees?
For flower beds and around shrubs, 2–3 inches is the standard recommendation — enough to suppress weeds and retain moisture without smothering roots. Around trees, a 3–4 inch depth in a ring (keeping mulch away from the trunk) helps regulate soil temperature. Going deeper than 4 inches can cause root rot and create habitat for pests. Refreshing mulch annually with a 1-inch top-up is more effective than a single thick application.
Why do I need to add a wastage factor when calculating mulch?
Mulch compresses during transport and settling, meaning a delivered cubic yard takes up slightly less space once laid. Irregular bed shapes, sloped terrain, and spreading overlap also consume more material than a simple rectangle calculation predicts. A 5–10% wastage factor compensates for these real-world losses. Without it, you risk running short mid-project and paying delivery fees for a small top-up order.