Garden Mulch calculator
Mulch is sold in 2 cubic foot bags and in cubic yards, and one cubic yard is 13.5 bags. The crossover where bulk becomes cheaper usually arrives sooner than people expect — often around two cubic yards, or roughly 27 bags.
How this is calculated
Cubic feet = area (sq ft) × depth (in) ÷ 12. Cubic yards = cubic feet ÷ 27. Bags = cubic feet ÷ bag size.
Source: Volume conversion; 3 in depth follows extension mulching guidance
Worth knowing: Never pile mulch against a tree trunk. "Mulch volcanoes" hold moisture against the bark, invite rot and rodents, and can kill a tree over several years. Keep mulch a few inches clear of trunks and stems, and cap total depth at about 4 inches — deeper starves roots of oxygen.
Common questions
How deep should mulch be?
Two to three inches for most beds, up to four where you are fighting weeds hard. Deeper than four inches starts to restrict oxygen and water reaching the roots, and can cause the surface to shed rain rather than absorb it.
When is bulk cheaper than bags?
Usually around two cubic yards. A cubic yard is 13.5 of the standard 2 cubic foot bags, so bulk delivery often costs less per yard once you are buying 25-30 bags — before you count the trips and the plastic.
Do I need to remove old mulch first?
Not usually. Old mulch breaks down into the soil, which is the point. Rake it to break up any matted crust, then top up to your target depth rather than adding a fresh full layer on top.
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