How much mulch do I need?

1. The three-step calculation

Mulch is the same volume calculation used for gravel, with the weight step swapped for a bag step — mulch is sold by volume, not by weight, because it is a light organic cover rather than dense aggregate.

1. Measure the bed. Length × width in feet (or metres). For a curved border or an odd shape, split it into rectangles and add them up, or treat a rough oval as length × width × 0.8.
2. Multiply by depth. Convert inches to feet first (3 in = 0.25 ft). That gives cubic feet; divide by 27 for cubic yards. Metric users: metres × metres × metres gives cubic metres directly.
3. Convert to bags. Divide the cubic feet by the bag size — usually 2 cubic feet for a standard North-American bag, or work in litres for bagged bark elsewhere (a cubic metre is 1,000 litres). Round up to whole bags.

Worked example, all the way through: a border 30 ft long and 4 ft wide, topped up 3 inches. Volume = 30 × 4 × (3 ÷ 12) = 30 cubic feet. Divide by 27 → 1.11 cubic yards. In standard bags, 30 ÷ 2 = 15 bags. Past a yard like this, a bulk delivery is usually the cheaper buy.

2. Coverage table — what one yard (or cubic metre) covers

Pure geometry: coverage = volume ÷ depth. These are planning figures for a level, evenly spread bed — real coverage drops a little over rough ground.

Bags-to-yard the other way round: a cubic yard is 27 cubic feet, so it holds about 14 standard 2-cubic-foot bags or 9 of the 3-cubic-foot bags. That is the number to weigh against a bulk price once your bed pushes past half a yard.

3. How deep should mulch be?

Depth is where most mulch orders go wrong, in both directions. Too thin — under an inch — and weeds push straight through and the soil dries out, which defeats the point. Too thick — much past four inches on a planted bed — and you can starve roots of air and hold so much water that you rot the very plants you are protecting. For most gardens, 2–3 inches (50–75 mm) is the honest sweet spot: enough to block light to weed seeds and slow evaporation, shallow enough to let water and air through to the roots. Coarse bark can sit a little deeper than fine, fast-rotting mulch because it lets more air through.

The single most common mistake is "volcano mulching" — heaping mulch up against a tree trunk or shrub stem in a cone. Bark needs to breathe and dry out; piled against living bark it traps moisture, invites rot and bores, and encourages roots to grow up into the mulch instead of down into the soil. Keep a clear ring of a few inches around every trunk and crown, and spread the mulch out flat like a doughnut, not up like a cone.

4. Bags or bulk, and which mulch to pick

Bags win for small beds: they are clean, easy to carry through a house or gate, and you buy exactly what you need. Bulk by the cubic yard wins on price and on speed for anything larger — but you need somewhere for the truck to tip it and a barrow to move it. The volume is identical either way, so the only real question is handling. As a rough rule, once a job needs more than ten or so bags, price up a bulk yard and compare. A pallet of bagged mulch commonly holds somewhere between 50 and 70 two-cubic-foot bags depending on the brand and bag size — confirm the exact count with your supplier rather than assuming.

Material changes the look and the lifespan, not the volume math. Shredded hardwood bark knits together and stays put on slopes; bark nuggets last longer but float and wash in heavy rain; straw and leaf mould break down fast and feed the soil but need topping up often; and inorganic options like stone or rubber never rot — for those, the gravel calculator handles the weight side. Whatever you choose, the calculator gives the cubic yards and bag count, and the rest of the landscaping tools cover the rest of the yard.

One honest caveat: organic mulch is a consumable, not a one-time install. It breaks down, composts into the soil and thins out over a season or two, so plan on a light top-up rather than a full re-do each year — a one-inch refresh covers more than three times the area of a fresh three-inch lay, which is why the coverage table above is worth keeping handy.

Common questions

How do I calculate how much mulch I need?

Volume = length × width × depth, with depth in the same unit (3 inches = 0.25 ft). The result is cubic feet; divide by 27 for cubic yards. To count bags, divide the cubic feet by the bag size — about 2 cubic feet for a standard bag.

How many bags of mulch are in a cubic yard?

A cubic yard is 27 cubic feet. With standard 2-cubic-foot bags that is about 14 bags (27 ÷ 2 = 13.5, rounded up); with 3-cubic-foot bags, 9 bags. That is the break-even worth knowing — past roughly half a yard, bulk is usually cheaper than bags.

How many square feet does a yard of mulch cover?

At 2 inches deep, about 162 square feet; at 3 inches, about 108; at 4 inches, about 81 (a cubic yard is 27 cubic feet, and coverage = 27 ÷ depth in feet). Deeper means less coverage in direct proportion.

How much extra mulch should I order?

Mulch has no cut-offcut waste like tile, so you do not need a big margin — but it settles after spreading and beds are rarely perfectly level, so rounding bulk up to the next quarter-yard, or adding a bag or two, is sensible. Top-ups each season are normal as organic mulch breaks down.