Mulch Calculator

Cubic yards and bags of mulch for beds and landscaping. Updated for 2026.

Last reviewed July 2026 · Free · Nothing you enter is stored

How this calculator works

Cubic yards = square feet × depth in inches ÷ 324 — the same volume math as gravel. Bag counts assume the standard 2 cu ft bag (13.5 bags per cubic yard). Bulk mulch averages about $50 per cubic yard for material; bagged mulch typically costs 2–3× more per yard equivalent but is easier to handle for small jobs.

The waste allowance

Mulch is one of the few materials where the calculator does not add a waste allowance, because there is almost nothing to waste. What comes off the truck goes on the bed, and anything left over gets spread somewhere else. The failure mode here runs in the opposite direction: people order generously, spread the surplus rather than store it, and end up with beds far deeper than they intended. Depth is the number that matters, and going over it does real damage to plants. The only rounding worth doing is up to the next whole bag or the next whole cubic yard, because suppliers do not sell fractions, and mulch settles by a noticeable amount over the first few weeks as it knits together and begins to break down.

The volume maths, and what a yard actually covers

A cubic yard is 27 cubic feet. Spread one inch deep that covers 324 square feet, so coverage at any other depth is simply 324 divided by the depth in inches. At two inches a yard covers 162 square feet; at three inches it covers 108. None of this is disputed or approximate. It is the definition of a cubic yard, and any supplier quoting different coverage is quoting a different depth.

Bagged mulch is usually sold in two cubic foot bags, which works out at 13.5 bags to the cubic yard. That conversion is the one worth keeping in your head at the garden centre, because it is where bulk delivery starts to look sensible. Ten or twelve bags is a car boot and an afternoon; forty bags is most of a yard and a half, hauled one at a time, at a price per yard that is usually well above what a bulk load costs delivered.

The practical approach is to measure each bed as a rectangle, add the rectangles together, and accept the small overestimate that curved edges introduce. Landscape beds are rarely regular, and trying to calculate the true area of a kidney-shaped bed gains you very little against the settling and the rounding you will do anyway.

How deep, and what the extension guidance says

Penn State Extension recommends two to four inches of mulch on well-drained soil. For finely textured mulches, the recommendation drops to one to two inches, because fine material packs down tightly and a deep layer of it behaves quite differently from the same depth of coarse bark. Fine mulch at four inches can shed water rather than admit it, which is the reverse of what mulch is there to do.

Three inches is a reasonable default for a new bed of ordinary shredded hardwood: enough to suppress most annual weeds and to slow evaporation, without approaching the depth at which the layer starts to work against the plants. Two inches is generally sufficient when topping up an existing bed.

The same guidance is emphatic on one point that has nothing to do with depth over the bed as a whole. Mulch should be kept off the trunk, and the root flare, the point where the trunk widens as it meets the ground, should remain visible. The phrase extension services use is mulch out, not up: extend the ring outward to cover more of the root zone rather than building it higher against the stem.

What over-mulching actually does

Too much mulch deprives roots of oxygen. Roots respire, and a thick, wet, decomposing blanket over them restricts the gas exchange they depend on, which is why declining trees in over-mulched beds often produce fine roots growing up into the mulch layer itself rather than down into the soil where they belong.

Bark kept permanently damp begins to decay. Bark is a plant's protective layer and it is adapted to being exposed to air, not buried. Constant moisture against it leads to decay of the bark tissue, and the resulting wounds leave the plant far more susceptible to disease and fungal infection than it would otherwise be.

Deep mulch is also a habitat. Voles nest in it and gnaw at bark through the winter under cover, and termites and carpenter ants find it a convenient bridge and harbourage, which is the reason mulch should be held back from house siding as well as from trunks. On top of that, a decomposing pile generates real heat: temperatures inside can reach around 140 degrees Fahrenheit, which is high enough to damage the tissue it is piled against.

Refreshing beds without compounding the depth

Mulch is usually topped up annually, and this is where beds quietly get into trouble. Adding two or three inches every spring onto a layer that has only partly broken down compounds year on year, and after several seasons the bed is six or eight inches deep with the crowns of the shrubs buried somewhere in the middle of it.

The habit worth building is to check the existing depth before ordering anything. If the bed still has two or three inches on it, the fix is to break up the crust with a rake, which restores the appearance and lets water through, rather than to buy more material. Where the layer has genuinely thinned, top up only to the target depth.

Where beds have already been built up too far, pulling the excess back is worth the afternoon it takes, particularly around trees. Clear the mulch away from the trunk until the root flare is exposed and the trunk visibly widens where it enters the ground. Piling mulch against the trunk, the practice known as volcano mulching, is described by Penn State Extension as one of the most common tree-killing mistakes in residential landscaping, and it is entirely reversible up until the point that the damage is done.

Mulch coverage by depth

All coverage figures follow from a cubic yard being 27 cubic feet, or 324 square feet at one inch deep. Bag counts assume the standard two cubic foot bag, at 13.5 bags per cubic yard.

Coverage is arithmetic from the definition of a cubic yard. Recommended depths of two to four inches on well-drained soil, and one to two inches for finely textured mulch, are from Penn State Extension, which is also the source for the guidance on keeping mulch off the trunk and exposing the root flare.

What goes wrong in mulched beds

Volcano mulching. Piling mulch into a cone against the trunk holds moisture on the bark and buries the root flare. Penn State Extension calls it one of the most common tree-killing mistakes in residential landscaping.

Adding a full depth every year. New mulch laid over old that has not broken down compounds the depth season after season. Check what is already there and top up only to the target depth.

Treating all mulch the same. Finely textured material packs tightly and belongs at one to two inches. Applied as deep as coarse bark it sheds water instead of letting it through.

Running mulch up against the house. Deep mulch against siding harbours termites and carpenter ants and blocks the inspection gap. Hold it back from the foundation.

Assuming deeper means better weed control. Past about four inches the added suppression is marginal while the cost to the plants is not. Oxygen starvation, bark decay and heat from decomposition all scale with depth.

Frequently asked questions

Why your state changes the price (but not the quantity)

How much mulch you need is physics — it doesn't care where you live. What it costs does. Labor rates, delivery distance, fuel, and local demand move installed prices by roughly 45 points from end to end: Arkansas, Mississippi, North Carolina sit near the bottom of the range, while Alaska, Hawaii, New York sit at the top. The Price this for selector at the top of the calculator applies a published construction cost index for your state to the 2026 national averages, so the dollar figures move and the material list stays put.

Treat the result as a budgeting range, not a quote. Two metros inside the same state can differ by more than the statewide index suggests, and a single busy contractor can outweigh both. See the full cost index for all 50 states and where the price data comes from.