How to calculate mulch
Mulch is sold by volume. Multiply the bed area by the depth — converted to feet — to get cubic feet, then divide by 27 for cubic yards:
Cubic yards = (Length × Width × Depth ÷ 12) ÷ 27
A 20 × 10 ft bed at 3 inches deep is 200 × 0.25 = 50 cubic feet, or about 1.85 cubic yards. At 2 cubic feet per bag, that's 25 bags.
Bags vs. bulk
A cubic yard is 27 cubic feet, so about 13.5 bags (2 cu ft each) equal one yard. Bags are handy for small beds, but past roughly two cubic yards — about 27 bags — bulk delivery is usually much cheaper.
How deep to spread it
Aim for 2–3 inches in beds and 3–4 inches around trees and shrubs, keeping mulch a few inches off trunks and stems. Top up about an inch each spring as the old layer breaks down rather than replacing it all.
Frequently asked questions
How much mulch do I need?
Multiply the bed area by the depth in feet to get cubic feet, then divide by 27 for cubic yards. A 20 × 10 ft bed at 3 inches deep is 200 sq ft × 0.25 ft = 50 cubic feet, or about 1.85 cubic yards.
How many bags of mulch are in a cubic yard?
Bagged mulch is usually sold in 2-cubic-foot bags, and a cubic yard is 27 cubic feet — so about 13.5 bags fill a cubic yard. Once you need more than roughly two cubic yards, bulk delivery is usually cheaper than buying bags.
How deep should mulch be?
Two to three inches is right for most beds — enough to suppress weeds and hold moisture without smothering roots. Use 3 to 4 inches around trees and shrubs, but keep mulch a few inches away from trunks and stems to prevent rot.
Should I buy bags or bulk mulch?
Bags are convenient for small beds and easy to carry, but they cost more per cubic foot. For larger projects, bulk mulch delivered by the cubic yard is far cheaper — the break-even is usually around two cubic yards, or about 27 bags.
How often should I replace mulch?
Organic mulch breaks down over time, so most beds need a fresh top-up once a year, usually in spring. You often only need to add an inch or so to restore the depth rather than replacing it all — measure the existing depth first.
Disclaimer: Results are estimates for planning. Coverage varies with how firmly mulch is packed and settling over time — confirm quantities with your supplier.