How to Calculate Mulch Quantity
Bed area × depth, converted to cubic yards or bags
Area times depth
Measure the bed's area (length × width for a rectangular bed, or break an irregular bed into sections), then multiply by the depth. Iowa State University Extension notes that many hardwood chipped or shredded mulches are spread 2 to 4 inches thick. Around trees, UVM Extension advises no more than 2 to 4 inches, with mulch kept off the trunk and the root flare left visible.
Converting to cubic yards
Convert your depth to feet (2 in = 0.167 ft) and multiply by area in square feet to get cubic feet, then divide by 27 to get cubic yards — bulk mulch is typically sold and delivered by the cubic yard.
A shortcut: cubic yards = area (ft²) × depth (in) ÷ 324, because one cubic yard spread 1 inch deep covers 324 ft² (27 ft³ × 12).
| Depth | Area one cubic yard covers |
|---|---|
| 1 in | 324 ft² |
| 2 in | 162 ft² |
| 3 in | 108 ft² |
| 4 in | 81 ft² |
Or convert to bags
Divide the total cubic feet by the bag size printed on the label. For the common 2 ft³ bag, one cubic yard is 13.5 bags.
Worked Example
A 200 ft² bed, 3 inches deep.
Depth in feet: 3 ÷ 12 = 0.25 ft
Volume: 200 × 0.25 = 50 ft³
Cubic yards: 50 ÷ 27 ≈ 1.85 yd³
Or in bags (2 ft³ each): 50 ÷ 2 = 25 bags
With the Mulch Calculator's 5% default allowance: 1.85 × 1.05 ≈ 1.94 yd³, or 26.25 → 27 bags of 2 ft³
FAQ
- How much area does a yard of mulch cover?
- One cubic yard covers 324 ft² at 1 inch deep, so 162 ft² at 2 inches, 108 ft² at 3 inches and 81 ft² at 4 inches.
- How many bags of mulch are in a cubic yard?
- A cubic yard is 27 cubic feet, so it is 13.5 bags of 2 cubic feet. For other sizes, divide 27 by the bag size on the label.
- How deep should mulch be?
- Iowa State University Extension notes that hardwood mulches are often spread 2 to 4 inches thick, and UVM Extension advises no more than 2 to 4 inches around trees, kept off the trunk.
Related Calculators
Related Guides
Sources
NIST SP 811
Unit conversion reference (cubic feet, cubic yards, cubic metres).
NIST SP 811 — referenceIowa State University Extension, How to determine the amount of mulch needed for a garden bed
Area × depth formula, 2–4 in for hardwood chipped or shredded mulches, and dividing by the bag size.
Iowa State University Extension, How to determine the amount of mulch needed for a garden bed — referenceUVM Extension, Beware the mulch volcano
No more than 2 to 4 inches around trees; keep mulch off the trunk and the root flare visible.
UVM Extension, Beware the mulch volcano — reference