Mulch Calculator

Quick answer: one cubic yard of mulch covers 324 square feet one inch deep — so 108 sq ft at 3 inches, 162 sq ft at 2 inches (Clemson Cooperative Extension). A cubic yard is 27 cubic feet, which is 13½ bags of 2 cu ft (14, since you cannot buy half a bag). Clemson gives 2–3 inches for bark, wood chips, pine needles and shredded leaves, 2 inches for grass clippings and 1 inch for stone — and says to keep all of it 2 to 3 inches clear of stems and trunks.

How to use it

Measure the bed, pick the shape it is closest to, and choose a depth. The answer comes in cubic yards, because that is what a landscape supplier sells and quotes in, and in bags, because that is what you would otherwise be counting in a car park. If you are mulching a tree, use the Tree ring shape — it takes the trunk out of the middle, which matters more than you would think on a small ring.

Type a price and it multiplies for you. This page carries no prices of its own: mulch is local, it moves with the season, and a stale number in a calculator is worse than no number at all.

How much a yard covers, at every depth

The arithmetic is the one Clemson prints: work out the square footage, multiply by the depth in inches, divide by 324, and you have cubic yards. The calculator above does it with the shapes filled in.

How deep, by material

Depth is not a matter of taste. Too thin and weeds come through; too thick and water and air stop reaching the roots, which is the thing that actually kills plants in a well-mulched bed. These are Clemson’s published figures:

Rubber mulch is not on that list because no extension service publishes a depth for it, so this page does not invent one — read your bag. It also never breaks down, which is either the point or the problem depending on how you feel about still having it there in ten years.

The mulch volcano, and why it matters

The single most expensive mulching mistake is piling it in a cone against a tree trunk. Clemson’s instruction is to keep mulch 2 to 3 inches away from the stems of woody plants, “to prevent decay caused by wet mulch and rodent damage during the winter”. Bark that stays wet rots; mice and voles nest in the mulch and chew the bark over the winter; and roots grow into the mulch and circle the trunk instead of spreading. A doughnut with a clear well at the centre does everything you want mulch to do. A volcano kills the tree slowly enough that nobody connects the two. Keep it 6 to 12 inches away from the walls of buildings as well.

Bags or bulk?

The crossover is usually somewhere around two cubic yards. Below that, bags are easier to handle, easier to store and you can buy them as you go. Above it, bulk is cheaper by a wide margin and the delivery fee stops mattering — a yard is about 14 two-cubic-foot bags, so three yards is more than forty bags to lift twice. Work out the volume above first, then price both; the calculator will do the multiplication for whichever one your supplier quotes.

One thing that catches people: bagged mulch is sold by volume, not weight, and a wet bag and a dry bag hold the same amount of mulch. Bulk is normally sold by the yard, but some suppliers price by the ton, and the weight of a yard changes with how wet it is — ask which they mean before you compare two quotes.

Order a little over, not a little under

Nothing here adds a waste factor, because there is no published figure for one and an invented 10% is just a number somebody made up. What experience says is simpler: mulch settles, beds are never quite the shape you measured, and the second trip costs more than the extra bag. If the answer lands at 9.4 bags, buy ten.