Mulch Calculator: How Much Mulch Do I Need?

Yards and bags, side by side

Bulk mulch is sold by the cubic yard. Bagged mulch is sold by the cubic foot. One yard is 27 cubic feet (a cube 3 feet on every side), so the conversion is short: 13.5 bags at 2 cubic feet, or 9 bags at 3 cubic feet, per yard. Bags are also not all the same size, which is why the calculator takes your own bag size. Read the label before you trust a count.

The number that matters for planning is how far each unit spreads. Coverage is inversely tied to depth: double the depth and each yard or bag covers half the ground.

Worked example: a 300 square foot planting area at 3 inches is 300 × 3 ÷ 324 = 2.78 yards. Add a 10 percent cushion and it is 3.06 yards, which is 42 bags at 2 cubic feet or 28 bags at 3 cubic feet. The smaller job, one 10 by 4 foot bed at 3 inches, is 10 cubic feet: 5 of the 2 cubic foot bags, or 4 of the 3 cubic foot bags.

Depth by material

Fine-textured mulch, double-shredded hardwood and dyed hardwood, packs tight and does its job at 2 to 3 inches. Coarse mulch, pine bark nuggets and pine needles, leaves gaps and wants 3 to 4 inches. Those are the ranges on our mulch for weed control page, and Clemson’s Home & Garden Information Center lands in the same place: fine-textured mulches no deeper than 2 to 3 inches, coarse mulches up to 4. The calculator starts at the middle of each range (2.5 and 3.5 inches) and you can overwrite it.

Settling: how much extra to order

Mulch does not stay at the depth you spread it. The University of Florida’s landscape mulch settling trial laid 3.5 inches (9 cm) of six mulches in a field and measured for two years. Pine bark and cypress kept about 6 of the 9 cm, roughly two thirds. Pine straw fell to half its depth in the first year and was down to about 1 cm by year two. It is one Florida site, so treat the exact figures as a direction, but the order holds anywhere: needles and leafy mulches sink fastest, woody mulches hold longest.

That is why the calculator adds a 10 percent cushion by default. Our own rule of thumb on the weed control page, 100 square feet per yard instead of the raw 108 at 3 inches, builds in about 7 percent. If you are buying pine needles, use the 15 or 20 percent setting, or start a half inch deeper than the range says.

Too much is a real problem

Ordering extra to be safe has a ceiling. Penn State Extension says to apply a 2 to 4 inch layer of organic mulch and no more, and to use 1 to 2 inches when the mulch is fine or double-shredded because it lets less oxygen through. Extension sources differ a little on fine mulch (Clemson says 2 to 3 inches, Penn State says 1 to 2 for trees), so the low end of our range is the safe pick on soil that drains slowly. Washington State Extension warns that excessive fine-textured mulch can suffocate plant roots and that mulch should never be piled against a trunk like a volcano; it recommends starting 6 inches from the trunk.

The math shows what over-mulching costs in truckloads too. That 300 square foot area takes 2.8 yards at 3 inches and 5.6 yards at 6 inches, twice the mulch for a layer that works against the plants. If you are mulching around trees, subtract the bare ring at the trunk from your bed area before you enter it.

When bulk delivery or blowing beats bags

Bags win on small jobs: a single bed, a top-up of one foundation strip, anything under about 3 yards where you can carry it from the car. Above that, the arithmetic turns. Five yards is 68 bags at 2 cubic feet, every one lifted out of a vehicle and cut open. Use the price check in the calculator with your own numbers: bag price times bag count against yards times the bulk price plus delivery. Delivery fees are a fixed cost, so they shrink per yard as the order grows.

Past that, method matters as much as material. For our crews, hand spreading is often cheaper until roughly 10 to 15 yards, and above that blowing through a hose comes out ahead on time and cost; the full comparison, including the 150 foot hose reach, is in mulch blowing vs. hand spreading. A finished depth is a probe measurement, not an eyeball, and blowing does not change the yardage math on this page.