How much mulch for 1000 square feet?

How the number is worked out

Volume is bed area × depth, with the depth converted from inches to feet. A 100 sq ft bed at 3 in is 100 × 0.25 = 25 cubic feet, or 0.93 cubic yards.

The figure worth remembering is the other way round. A cubic yard is 27 cubic feet, so spread at a depth of d inches it covers 324 ÷ d square feet:

• 2 in → 162 sq ft
• 3 in → 108 sq ft
• 4 in → 81 sq ft

Why "one yard covers 100 square feet" is not an answer

That rule of thumb is everywhere, and it is a rounded-down version of the 3 in figure. It happens to be about 7% conservative at 3 in, which is harmless. The problem is that it gets quoted with no depth attached, and people apply it at 4 in — where a yard reaches only 81 sq ft. On a 400 sq ft bed that is the difference between four yards and five.

Any mulch coverage number without a depth beside it is incomplete. That is the single most common error on competing calculators.

How deep to go

Penn State Extension and Ohio State University Extension both put the working range at 2–3 inches: enough to hold moisture and block light, shallow enough to let water and air through to the roots. More than 4 inches encourages adventitious roots that grow out of the trunk instead of the root system, and over time those can girdle the tree.

Around a tree, keep mulch off the bark entirely and leave the root flare visible. The common shorthand is 3-3-3 — at least 3 in back from the trunk, no more than 3 in deep, out to a 3 ft diameter.

If you are topping up existing mulch, measure what is already there first. Most beds only need an inch to look new, and mulch piled year on year is how beds end up 6 in deep.

Bags or bulk

The standard US retail bag holds 2 cubic feet, so a cubic yard is 13.5 bags. Bark nuggets often come in 3 cu ft bags (9 per yard) and some premium cedar in 1.5 cu ft (18 per yard) — the number on the bag is the only thing that settles it.

Bulk becomes the obvious choice somewhere around 3 cubic yards, which is 40-odd bags. Shredded bark is 400–700 lb per cubic yard dry, and over 800 lb after rain, so a half-ton pickup takes about one yard at a time, not two.

What this does not include

• Settling and decomposition. Organic mulch loses roughly an inch a season.
• Edging. Without a hard edge, mulch migrates onto the lawn and out of the bed.