The formula
Volume in cubic feet = length × width × depth in inches ÷ 12. Divide by 27 to get cubic yards. One cubic yard is 27 cubic feet, so it fills fourteen 2-cubic-foot bags or nine 3-cubic-foot bags, rounded up — you cannot buy part of a bag.
Worked example
| Bed | Depth | Cubic yards | 2 cu ft bags | 3 cu ft bags |
|---|---|---|---|---|
| 20 ft × 4 ft | 3 in | 0.74 | 10 | 7 |
| 10 ft × 10 ft | 2 in | 0.62 | 9 | 6 |
Depth is the decision that matters
Two inches suppresses weeds poorly and breaks down within a season. Three inches is the usual recommendation for bark and wood mulch, and four inches suits coarser material. Going deeper than that can hold too much moisture against stems and trunks, so keep mulch pulled back from the base of plants.
Bags versus bulk
Below about one cubic yard, bags are usually the simpler buy. Above it, a bulk delivery priced per yard is almost always cheaper — and the cubic-yard figure is exactly what a landscape supplier asks for. Add a little for oddly shaped beds, since the calculator assumes a clean rectangle.
Related guides
Frequently asked questions
How deep should mulch be?
About 3 inches for most bark mulches. Check the product, since fine mulches settle more than coarse ones.
Why are the bag counts rounded up?
Because volume left over still needs a whole bag. The cubic-yard figure is left unrounded so you can order bulk precisely.
Does this work for topsoil or compost?
Yes. The volume arithmetic is identical; only the recommended depth changes.