How volume is calculated
Area = length × width (circle: π × (diameter ÷ 2)²)
Cubic feet = area × depth(in) ÷ 12
Cubic yards = cubic feet ÷ 27
Bags = cubic feet ÷ bag size, rounded up
One cubic yard is 27 cubic feet, so it covers 324 sq ft at 1 inch, 108 sq ft at 3 inches. Bagged products state their volume on the bag (commonly 1.5, 2 or 3 cu ft). Settling and compaction mean you may want a little extra for soil and compost.
Worked example
A 30 × 4 ft border mulched 3 inches deep:
| Area | 120 sq ft |
|---|---|
| Volume (120 × 3 ÷ 12) | 30 cu ft |
| Cubic yards | 1.11 |
| 2 cu ft bags | 15 |
For gravel or stone sold by the ton, ask your supplier for the product’s weight per cubic yard — it varies with the material and size.
Frequently asked questions
How many bags of mulch in a yard?
A cubic yard is 27 cu ft: 13.5 bags of 2 cu ft, or 9 bags of 3 cu ft.
How deep should mulch be?
It depends on the material, the plants and your climate. Keep mulch pulled back from plant stems and tree trunks, and ask your local cooperative extension office for guidance for your area.