How to calculate mulch
cubic yards = L (ft) × W (ft) × (depth in ÷ 12) ÷ 27
Multiply the bed area by the depth to get volume. Bulk mulch is sold by the cubic yard in the US and Canada, and by the cubic meter in Australia. Bags are labeled in cubic feet or liters.
Worked example
A 20 × 10 ft bed at 3 inches deep: 200 sq ft × 0.25 ft = 50 cu ft, which is 1.85 cubic yards, or 25 bags of 2 cu ft.
How deep should mulch be?
| Job | Depth |
|---|---|
| Topping up existing mulch | 1 in (2–3 cm) |
| Most flower and shrub beds | 2 to 3 in (5–8 cm) |
| New beds, weed suppression | 3 to 4 in (8–10 cm) |
Deeper is not always better. Thick layers can keep soil too wet and stop water reaching roots. Keep mulch a few inches away from tree trunks and plant stems; piling it against the bark encourages rot.
Bags or bulk?
A cubic yard equals 13.5 bags of 2 cu ft. Bags are easy to carry and store, but once a job needs more than a couple of cubic yards, bulk delivery is usually cheaper. Compare the price per cubic yard, and ask about the delivery charge.
Round and irregular beds
For a round bed, the area is 3.14 × radius². Enter that area as length with a width of 1. For curved beds, estimate an average length and width, or split the bed into simpler shapes.
Frequently asked questions
How many bags of mulch are in a yard?
One cubic yard holds 13.5 bags of 2 cu ft, or 9 bags of 3 cu ft.
How much area does one yard of mulch cover?
At 3 inches deep, a cubic yard covers about 108 sq ft. At 2 inches it covers about 162 sq ft.
Can I use this for gravel or topsoil?
Yes, the volume is the same. Gravel and soil are much heavier than mulch, so ask your supplier for weight per yard before loading a trailer.
How often should I replace mulch?
Organic mulch breaks down over time. Most gardeners top it up by about an inch each year rather than replacing it completely.