How Much Mulch Do I Need? Depth, Coverage & Bags

Quick answer: measure each bed's area in square feet, pick a depth of 2–3 inches, and divide the area by the coverage for that depth — one cubic yard covers about 108 sq ft at 3 inches. Or skip the arithmetic and use the mulch calculator, which gives you both cubic yards and the number of bags. Here's how to get the depth and the order right.

How deep should mulch be?

Two to three inches is the sweet spot for most beds. Two inches is enough to suppress weeds; three gives you the best moisture retention and weed control. Less than that and weeds push through; more than about four inches and you start to starve roots of air and trap moisture against stems, which invites rot.

Spread it evenly and pull it back a couple of inches from trunks and stems — those "mulch volcanoes" piled against trees rot the bark. Because organic mulch breaks down over a season, most beds need a fresh 1–2 inch top-up each year rather than a full replacement.

How much does a yard of mulch cover?

Coverage depends entirely on depth. One cubic yard (27 cubic feet) spreads over:

• 162 sq ft at 2 inches
• 108 sq ft at 3 inches
• 81 sq ft at 4 inches

Double the depth and you halve the coverage — which is why getting the depth right matters for both your plants and your budget.

Bags vs. bulk

A standard bag of mulch holds 2 cubic feet, so it takes about 13.5 bags to make a cubic yard. Bagged mulch is convenient for one small bed or a top-up, but it costs several times more per yard than bulk. Once you need more than roughly ten bags, bulk delivery by the cubic yard is far cheaper. Use the cubic-yards figure to order bulk and the bag count for a quick garden-center run.

A worked example

You have two beds totaling 300 square feet and you want a 3-inch layer:

• Coverage at 3 inches: about 108 sq ft per cubic yard
• 300 ÷ 108 ≈ 2.8 cubic yards, or about 38 bags

Add roughly 10% to top up thin spots and edges. The mulch calculator does this live — enter your bed dimensions and depth and it returns yards, bags, and a recommended overage.

A note on material

Organic mulches (shredded hardwood, bark, wood chips) slowly break down and feed the soil, so they need topping up. Rubber mulch doesn't decompose but is heavier and doesn't improve the soil. If you're also filling or leveling beds underneath, the topsoil calculator covers the soil layer that goes below the mulch.