How to calculate mulch
Mulch is sold by the cubic yard in bulk, or in bags of 2 or 3 cubic feet. To find how much you need, multiply the area of the bed by the depth you want, in the same unit.
- Rectangular bed: length × width.
- Round bed or tree ring: π × radius².
- Triangular corner bed: ½ × the two sides that meet at the corner.
Worked example: a 10 × 10 ft bed at 3 in deep
100 sq ft × 0.25 ft = 25 cubic feet. That is 0.93 cubic yards, or 13 bags of 2 cu ft.
How deep should mulch be?
| Use | Depth |
|---|---|
| Flower and shrub beds | 2–3 in (5–7.5 cm) |
| Topping up existing mulch | 1–2 in (2.5–5 cm) |
| Paths and play areas (wood chips) | 3–4 in (7.5–10 cm), deeper under play equipment |
Deeper is not better in beds. Mulch piled too thick can keep soil soggy and starve roots of air. Keep it a few inches back from tree trunks and plant stems, and avoid the “mulch volcano” piled against the bark.
Building new beds? Fill them with soil first; the topsoil calculator works the same way.
Bags or bulk?
One cubic yard is 13½ two-cubic-foot bags. Bags are easier to move and store, so they suit small beds. Past about three yards, bulk delivery is usually cheaper, though many suppliers have a minimum order or delivery fee.