Mulch calculator: cubic yards, bags and the right depth

How deep should mulch be?

Two to four inches for most bark mulches. Below two inches, light reaches the soil and weeds germinate through it. Above four, water struggles to reach the soil and roots can be starved of air.

Finer material should go thinner than coarse. A finely shredded mulch at four inches mats together and sheds water; a coarse bark at four inches still breathes.

Depth	Coverage per cubic yard
1 in	324 sq ft
2 in	162 sq ft
3 in	108 sq ft
4 in	81 sq ft

Why you should never pile mulch against a trunk

The volcano of mulch heaped around a tree is the most common and most damaging mistake in landscaping, and it is worth saying plainly because it kills trees slowly enough that nobody connects the two.

Bark on a trunk is not adapted to constant moisture. Held against it, mulch keeps the bark permanently wet, which invites rot and boring insects. Worse, roots grow up into the mulch pile and circle the trunk, eventually strangling the tree from its own root system. The damage takes years to show.

Keep mulch three to six inches clear of the trunk. The shape you want is a doughnut, not a volcano.

How many bags in a cubic yard?

A cubic yard is 27 cubic feet, so 13.5 of the standard 2 cubic foot bags, or 9 of the 3 cubic foot bags. Bulk delivery is usually cheaper beyond about two yards, which is 27 bags, and considerably less work to carry.

Common questions

How much does a yard of mulch weigh?

Roughly 400 to 800 pounds dry for bark mulch, and up to 1,000 or more when soaked. Compost-based mulches are heavier than bark. These are supplier averages rather than standard figures: no standards body governs mulch density, and it varies with species and moisture more than anything else.

Should I remove the old mulch first?

Not usually. Bark mulch breaks down into the soil, which is part of the point. Top up to the depth you want rather than adding a full layer each year, or the total depth creeps past four inches over a few seasons without anyone noticing.

Does mulch stop weeds completely?

No, but three inches suppresses most germination from below. What it will not stop is seed landing on top of the mulch, which is why weeds appear in mulched beds anyway. They pull out easily, which is the real benefit.

Is rubber mulch a good idea?

It lasts far longer and does not need replacing, which is why it is common under playground equipment. It also adds nothing to the soil, can get very hot in direct sun, and is difficult to remove once it works into the ground. For planting beds, organic mulch feeds the soil as it breaks down and is generally the better choice.