Mulch coverage depends on two things: the volume printed on the bag and the depth of the new layer. A coverage label at 2 inches does not mean the same bag covers that area at 3 inches.
Coverage before any extra allowance
| Bag volume | 2 in deep | 3 in deep | 4 in deep |
|---|---|---|---|
| 1.5 cu ft | 9 | 6 | 4.5 |
| 2 cu ft | 12 | 8 | 6 |
| 3 cu ft | 18 | 12 | 9 |
For example, a 2 cu ft bag covers 12 sq ft at 2 inches, or 8 sq ft at 3 inches. Choose depth for the site; the table is arithmetic, not a depth recommendation.
Worked purchase example
A 200 sq ft bed needs 50 cu ft at 3 inches deep. Adding 10% makes 55 cu ft. In 2 cu ft bags, 55 ÷ 2 = 27.5, so buy 28 whole bags. That purchases 56 cu ft, leaving 1 cu ft beyond the allowance-adjusted estimate.
Refreshing existing mulch
If an existing layer is usable, measure it before adding more. Enter only the extra depth you need. Keep the ground you intend to leave clear around trunks out of the measured area.
Related: mulch depth and existing cover and bags vs bulk costs.
General guidance: adapt tasks to your local climate, plants and soil. Confirm product specifications with your supplier.