How to use the mulch calculator
- Measure each bed. For odd shapes, split the bed into rectangles and circles, run each one, and add the results. Or enter the total square feet directly.
- Choose a depth. A 2 to 4 inch layer is the range university extension services recommend. Use the low end for fine shredded mulch and for topping up old mulch.
- Enter bag and bulk prices to see which is cheaper for your job.
The formula
Cubic yards of mulch = area (sq ft) × depth (in) ÷ 324. The 324 comes from 27 cubic feet per yard × 12 inches per foot, and Clemson's Home and Garden Information Center uses the same rule: one cubic yard covers 324 square feet at 1 inch deep.
For bags, take cubic feet (cubic yards × 27) and divide by the bag size, then round up.
Worked example: a 20 × 5 ft bed, 3 inches deep
100 sq ft × 3 ÷ 324 = 0.93 cubic yards, or 25 cubic feet. That is 13 bags of 2 cu ft or 9 bags of 3 cu ft before any extra.
How far mulch goes
| Depth | 1 cubic yard covers | 2 cu ft bag covers | 3 cu ft bag covers |
|---|---|---|---|
| 1 in | 324 sq ft | 24 sq ft | 36 sq ft |
| 2 in | 162 sq ft | 12 sq ft | 18 sq ft |
| 3 in | 108 sq ft | 8 sq ft | 12 sq ft |
| 4 in | 81 sq ft | 6 sq ft | 9 sq ft |
Mulch needed for common bed sizes
At 3 inches deep, no extra added.
| Bed | Cubic yards | 2 cu ft bags | 3 cu ft bags |
|---|---|---|---|
| 4 × 8 ft bed | 0.3 | 4 | 3 |
| 5 × 20 ft border | 0.93 | 13 | 9 |
| 10 × 10 ft bed | 0.93 | 13 | 9 |
| 10 × 20 ft bed | 1.85 | 25 | 17 |
| 20 × 25 ft area | 4.63 | 63 | 42 |
Mulching tips
- Keep mulch pulled back a few inches from tree trunks and plant stems. Piling it against bark holds moisture where it can cause rot.
- More is not better. Layers deeper than about 4 inches can starve roots of air and water.